Liquid crystal display device having particular pixel region

ABSTRACT

A liquid crystal display device having first and second substrates, a liquid crystal composition layer provided between the first and second substrates, at least two video signal lines and a scanning signal line formed between the first substrate and the liquid crystal composition layer, and at least a counter electrode formed between the first substrate and the liquid crystal composition layer. An area between the two video signal lines include a first, second and third region extending along the video signal lines. The third region is arranged around the scanning signal line, and the first and second region have electrodes therein with the number of electrodes in the first region being different from the number of electrodes in the second region.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 09/234,494, filedJan. 21, 1999, now U.S. Pat. No. 6,341,003, the subject matter of whichis incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device and,more specifically, to a liquid crystal display device in which a pair ofinsulating substrates are opposed to each other via a predetermined gapthat is maintained by spacers, a liquid crystal composition (a liquidcrystal molecule) is held in the gap, and a storage capacitor portion isformed in each pixel region.

2. Description of the Related Art

High-resolution liquid crystal display devices capable of color displayfor use in notebook-sized computers and computer monitors are now widelyutilized.

Basically, in this type of liquid crystal display device, what is calleda liquid crystal panel is formed by holding a layer of a liquid crystalcomposition between two insulating substrates (hereinafter also referredto simply as substrates) such as glass plates at least one of which istransparent. This type of liquid crystal display device is generallyclassified into a type (simple matrix type) in which an image is formedby changing the orientation directions of liquid crystal molecules ofdesired pixels by selectively applying voltages to various electrodesfor pixel formation that are formed on the insulating substrates of theliquid crystal panel and a type (active matrix type) in which variouselectrodes for pixel formation and active elements for pixel selectionare formed and an image is formed by changing the orientation directionsof liquid crystal molecules of desired pixels by making selections fromthe active elements.

In general, the active matrix liquid crystal display device employs thatis called a vertical electric field type in which electric fields aredeveloped between electrodes formed on one substrate and an electrodeformed on the other substrate.

On the other hand, the liquid crystal display device of what is called alateral electric field type (also called as In-Plane Switching type,abbreviated as “IPS type” hereinafter) has been put into practical usein which the directions of electric fields that act on the liquidcrystal layer are approximately parallel with the substrate surfaces. Inan example of the lateral electric field type liquid crystal displaydevice, a very wide viewing angle is obtained by forming comb-teethelectrodes for electric field formation on one of the two substrates.

In the lateral electric field liquid crystal display device, an activematrix substrate is provided with scanning signal lines and video signallines, switching elements formed in the vicinity of the crossing pointsof the scanning signal lines and the video signal lines, pixelelectrodes to which drive voltages are applied via the respectiveswitching elements, and counter electrodes that are formed in the sameplane as the pixel electrodes. A color filter substrate is provided witha black matrix made of a resin composition and color filter layersformed for each pixel in an opening region of the black matrix. A liquidcrystal panel is formed by holding a liquid crystal composition betweenthe active matrix substrate and the color filter substrate. The liquidcrystal display device is configured in such a manner that a backlightis disposed in the rear of the liquid crystal panel and a unifiedstructure is obtained by using top and bottom cases.

Image display is performed by changing the light transmittance of theliquid crystal compound by electric field components that are formedbetween the pixel electrodes and the counter electrodes so as to extendapproximately parallel with the substrate surfaces.

In contrast to the vertical electric field type one, the lateralelectric field type liquid crystal display device is superior in viewingangle; that is, it allows a user to view a clear image even when he islocated at a position that forms a large angle with the display screen.

The liquid crystal display device having the above configuration isdisclosed in Japanese Unexamined Patent Publication No. Hei. 6-160878and its counterpart U.S. Pat. Nos. 5,598,285, and 5,737,051, forexample.

FIG. 1 is a plan view showing one pixel, a light shield region of ablack matrix BM, and its vicinity of a conventional lateral electricfield type liquid crystal display device.

As shown in FIG. 1, each pixel is provided in a region enclosed by foursignal lines that cross each other, that is, a scanning signal line(gate signal line or horizontal signal line) GL, a counter voltagesignal line CL, and two adjacent video signal lines (drain signal lineor vertical signal line DL.

Each pixel includes a thin-film transistor TFT, a storage capacitorportion Cstg, a pixel electrode PX, and an counter electrode CT. In FIG.1, a plurality of scanning signal lines GL and counter voltage signallines CL are provided at the top and bottom of the pixel direction so asto extend in the right-left or horizontal direction. A plurality ofvideo signal lines DL are provided at the right-left side of the pixelso as to extend in the top-bottom or vertical direction. The pixelelectrode PX is connected to the thin-film transistor TFT, and thecounter electrode CT is integral with the counter voltage signal lineCL.

The pixel electrode PX and the counter electrode CT confront each other,and display is controlled by modulating transmission light or reflectionlight by controlling the orientation state of a layer of a liquidcrystal composition LC (hereinafter also referred to simply as a liquidcrystal or a liquid crystal layer) by means of an electric fielddeveloped between the pixel electrode PX and the counter electrode CT.Each of the pixel electrode PX and the counter electrode CT assumes acomb-teeth shape and has long and narrow portions extending in thetop-bottom or vertical direction in FIG. 1.

The pixel electrode PX and the counter electrode CT are formed in such amanner that the number P of comb-teeth portions of the pixel electrodePX and number C of comb-teeth portions of the counter electrode CT inone pixel necessarily satisfy a relationship C=P+1 (in FIG. 1, C=2 andP=1). The comb-teeth portions of the counter electrode CT and those ofthe pixel electrode PX are arranged alternately so as to have thecomb-teeth portions of the counter electrode CT arranged adjacent to thevideo signal lines DL. With this structure, shielding from electriclines of force originating from the video signal lines DL can beeffected by the counter electrode CT so that electric fields between thecounter electrode CT and the pixel electrode PX are not influenced bythe electric fields originating from the video signal lines.

The potential of the counter electrode CT is stable because it is alwayssupplied with a potential externally via the counter voltage signal lineCL. Therefore, the counter electrode CT has almost no potentialvariation even if it is adjacent to the video signal lines DL. Further,the above structure makes the geometrical position of the pixelelectrode PX more distant from the video signal lines DL, whereby theparasitic capacitances between the pixel electrode PX and the videosignal lines DL are greatly reduced and hence a variation of a pixelelectrode potential Vs due to video signal voltages can be controlled.

As a result, vertically extending crosstalk lines (an image qualityfailure called vertical smears) can be prevented.

In a specific construction, widths Wp and Wc of the pixel electrode PXand the counter electrode CT, respectively, are set at 6 μm, which issufficiently larger than 4.5 μm which is the maximum setting thicknessof a liquid crystal layer (described later). It is desirable that theelectrode widths Wp and Wc be sufficiently larger than 5.4 μm because itis preferable to provide a margin of 20% or more in view of processingvariations in manufacture. As a result, electric field componentsparallel with the substrate surfaces that are applied to the liquidcrystal layer become stronger than those perpendicular to the substratesurfaces, which prevents voltages for driving the liquid crystal tobecome unduly high. It is preferable that the maximum values of theelectrode widths Wp and Wc be smaller than an interval L between thepixel electrode PX and the counter electrode CT. This is because it theinterval between the electrodes is too short, electric lines of forceare curved sharply and hence regions where electric field componentsparallel with the substrate surfaces are stronger than thoseperpendicular to the substrate surfaces are made larger, as a result ofwhich the electric field components parallel with the substrate surfacescannot be applied to the liquid crystal layer efficiently. To give amargin of 20% to the interval L between the pixel electrode PX and thecounter electrode CT, it is necessary that the interval L be larger than7.2 μm. For example, in a case of constructing a liquid crystal displaydevice having a diagonal size of about 14.5 cm (5.7 inches) and aresolution of 640×480 dots, an interval L that is larger than 7.2 μm canbe realized by setting the pixel pitch at about 60 μm and dividing eachpixel into two parts.

To avoid disconnection, the electrode width of the video signal lines DLis set at 8 μm, which is somewhat larger than the widths of the pixelelectrode PX and the counter electrode CT. To avoid short-circuiting, aninterval of about 1 μm is provided between the video signal lines DL andthe counter electrode CT. The video signal lines DL and the counterelectrode CT are provided in different layers by forming the videosignal lines DL and the counter electrode CT above and below a gateinsulating film, respectively. On the other hand, the interval betweenthe pixel electrode PX and the counter electrode CT is changed inaccordance with the liquid crystal material used, for the followingreason. The electric field intensity for attaining the maximumtransmittance depends on the liquid crystal material. To obtain themaximum transmittance within the range of the maximum amplitude of asignal voltage that is set by the breakdown voltage of a video signaldriver circuit (signal-side driver) used, the electrode interval needsto be set in accordance with the liquid crystal material. The electrodeinterval becomes about 15 μm when a liquid crystal material that will bedescribed later is used.

In the example configuration being discussed, in a plan view of FIG. 1,a black matrix BM surrounds an opening of the pixel and is formed on thegate line GL, the counter voltage signal line CL, the thin-filmtransistor TFT, and the drain lines DL, and between the counterelectrode CT and the drain lines DL. The storage capacitor portion Cstgis located outside the opening of the black matrix BM (i.e., outside thepixel region) and is composed of the pixel electrode PX, the countervoltage signal line CL, and an insulating film formed between them.

In the liquid crystal display device, an alignment film is applied afterformation of the respective electrodes and electrode wiring lines,protective films, and insulating films and is given a liquid crystalalignment control ability by being subjected to a treatment calledrubbing.

In the conventional lateral electric field type liquid crystal displaydevice, since the storage capacitor portion Cstg is formed outside eachpixel region, there is no large hight change or steps in the pixelregion and hence the alignment film in the pixel region can be given auniform liquid crystal alignment control ability.

However, in recent years, liquid crystal display devices have beenproposed in which the aperture ratio of the entire screen is increasedby forming the storage capacitor portion Cstg in each pixel region. Inthose devices, the storage capacitor Cstg produces large steps in thepixel region and those steps may cause an alignment defect in a rubbingtreatment. As a result, what is called a domain occurs and causesdisplay unevenness.

In particular, alignment defects of the above kind occur frequently in acase where the multilayered film structure that constitutes the storagecapacitor portion Cstg has steps extending perpendicularly orapproximately perpendicularly to the alignment direction (rubbingdirection) of the alignment film. When such an alignment defect occurs,the liquid crystal does not operate normally in the vicinity of thestorage capacitor portion Cstg, to cause a domain. This results in aproblem that the contrast is lowered and display unevenness occurs,which means a marked reduction in image quality.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a liquid crystaldisplay device having good display quality by solving the above problemsin the art, specifically by decreasing the frequency of occurrence ofalignment defects that result from the presence of steps of the storagecapacitor portion Cstg formed in each pixel region and therebypreventing display failures such as a contrast reduction and displayunevenness.

To attain the above object, in the invention, edge sectional shapes ofsteps of a multilayered film structure formed in each pixel region(actually each opening region of a black matrix), in particular steps ofmultilayered films such as electrode that constitute a storage capacitorportion, are made gentle.

Specifically, the invention provides a liquid crystal display devicecomprising an active matrix substrate comprising a plurality of scanningsignal lines, a plurality of video signal lines, switching elementsformed in the vicinity of respective crossing points of the scanningsignal lines and the video signal lines, pixel electrodes to which drivevoltages are applied via the respective switching elements, counterelectrodes formed in a different plane than the pixel electrodes; acolor filter substrate comprising a black matrix made of a resincomposition, and color filter layers provided for respective pixelsformed in respective opening regions of the black matrix; a liquidcrystal composition held between the active matrix substrate and thecolor filter substrate; and storage capacitor portions located in therespective opening regions of the black matrix, each of the storagecapacitor portions being composed of a counter voltage signal line forsupplying a signal to an associated one of the counter electrodes, apixel electrode, and an insulating film provided between the countervoltage signal line and the pixel electrode, wherein image display isperformed by varying the light transmittance of the liquid crystalcomposition by electric field components that develop between the pixelelectrodes and the counter electrodes so as to extend approximatelyparallel with the substrate surfaces, and wherein one of a portion ofthe counter voltage signal line and a portion of the pixel electrodewhich form the storage capacitor have an outline within that of theother of the portion of the counter voltage signal line and the portionof the pixel electrode.

With the above configuration, the angles of steps in the storagecapacitor portions with respect to the surface of an alignment filmbecome gentle, whereby rubbing defects can be prevented from occurringin the vicinity of the storage capacitor portions. As a result, itbecomes possible to provide a liquid crystal display device having gooddisplay quality in which the frequency of occurrence of display failuressuch as a contrast reduction and display unevenness are greatly reduced.

In the above liquid crystal display device, most of a projected outlineshape of the portion of one of the counter voltage signal line and thepixel electrode arranged in an upper layer may be located inside aprojected outline shape of the portion of the other of the countervoltage signal line and the pixel electrode arranged in a lower layer.

In the above liquid crystal display device, most of a projected outlineshape of the portion of one of the counter voltage signal line and thepixel electrode arranged in a lower layer may be located inside aprojected outline shape of the portion of the other of the countervoltage signal line and the pixel electrode arranged in an upper layer.

With the above two features, the angles of steps of the electrode filmsconstituting the storage capacitor portions with respect to the surfaceof an alignment film become gentle, whereby rubbing defects can beprevented from occurring in the vicinity of the storage capacitorportions. As a result, it becomes possible to provide a liquid crystaldisplay device having good display quality in which the frequency ofoccurrence of display failures such as a contrast reduction and displayunevenness are greatly reduced.

These features can be not only applied to the pixel electrode and thepixel, but also to a pair of conductive layers extending in transversedirections and crossing one another in the pixel region and at least oneof the conductive layers including the branch portion extending from thecrossing in the direction of extension of the other of the conductivelayers within the pixel region. The pixel region is defined as a regionformed on the liquid crystal display substrate and transmitting light tobe modulated by the liquid crystal layer.

Where multilayered films such as electrode films, insulating films, andprotective films are formed in each pixel region, the invention is notlimited to the case where the multilayered films are ones belonging tothe storage capacitor portion.

The second object of the invention is to prevent the liquid crystaldisplay device from display failures caused by the reduction of thevoltage applied to its liquid crystal layer. This problem appears theliquid crystal display having such two kinds of conductive layersdefined as first and second conductive layers as follows. The first andsecond conductive layers are formed above a main surface of one ofsubstrates facing to the liquid crystal layer. The first conductivelayer extends in first direction, and has a first voltage. The secondconductive layer extends in second direction, and has a second voltage.Each of the first and second conductive layers has at least one portiontherefrom in a different direction and joined thereto at a corner, andis covered with an insulating film.

When the first voltage differs from the second voltage, the displayfailures appear in the liquid crystal layer. Namely, applying thedifferent electrical signals or voltages the first and second conductorsinduces this problem, even if the first and second conductive layers areisolated from one another by an insulating film, or are formed on themain surfaces of different substrates from one another.

To attain this object, the invention forms the corner with at least oneof a curve and at least one obtuse.

Specifically, the invention provides following two structures for theliquid crystal display device having a pixel electrode, an counterelectrode, and an counter voltage signal line for supplying a signal tothe counter electrode formed between a liquid crystal layer and one of apair of substrates sealing the liquid crystal layer therebetween.

One of the structures is described that the counter voltage signal lineextending in one direction crosses the pixel electrode extending in atransverse direction, at least one of the counter voltage signal lineand the pixel electrode has branch portions extending in the directionof extension of the other the counter voltage signal line and the pixelelectrode, and edges of the counter voltage signal line and the pixelelectrode with the branch portions thereof are connected with at leastone of a curve and at least one obtuse angle.

The other of the structures is described that the counter voltage signalline extending in one direction is connected to the counter electrodeextending in transverse direction to the one direction so as to connecttheir edges with at least one of a curve and at least one obtuse, andthe counter voltage signal line and the pixel electrode cross oneanother.

In both of the inventions, the pixel electrode, the counter electrode,the counter voltage signal line, and the substrate on which theseelectrodes and the signal line are covered with an insulating layer, andpreferably the insulating film formed on the pixel electrode isdifferent from that formed on the counter electrode and the countervoltage signal line. The crossing region in accordance to an overlappingof the counter voltage signal line and the pixel electrode is formed inthe light transmission region delimited by a light shielding material.

The detailed structures of this invention will be explained later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing one pixel, a light shield region of ablack matrix BM, and its vicinity of a conventional lateral electricfield type liquid crystal display device;

FIGS. 2(A)-2(C) is a sectional view of electrodes for one pixel (FIG.2(A)) and their vicinity (FIGS. 2(B), 2(C)) in an image display area andsubstrate peripheral portions of a liquid crystal panel that constitutesa lateral electric field type liquid crystal display device;

FIG. 3 is a sectional view of a thin-film transistor TFT;

FIG. 4 illustrates an angular relationship between the rubbing directionRDR and the applied electric field direction EDR;

FIG. 5 is a plan view showing the main part of peripheral portions of amatrix (AR) of a display panel including top and bottom substrates;

FIG. 6 is a sectional view of external connection terminals GTM to whicha scanning circuit is connected from the left side and its vicinity;

FIG. 7 is a sectional view of a tape carrier package shown in FIG. 6;

FIG. 8 is a general circuit diagram of an equivalent circuit of theliquid crystal display device according to the invention;

FIGS. 9(A)-9(F) are a drive waveform diagram of the liquid crystaldisplay device according to the invention;

FIGS. 10 through 12 show a manufacturing process of a liquid crystaldisplay device according to the invention;

FIG. 13 shows a notebook-sized personal computer that is an example ofan information apparatus in which a liquid crystal display device of theinvention is incorporated;

FIGS. 14(A)-14(C) are a plan view of the electrode structure forobtaining larger storage capacitance Cstg, a enlarged image of a part ofits uppermost surface after rubbing treatment, and an image of therubbing treatment around the storage capacitance, respectively;

FIGS. 15 is the other plan view of the electrode structure for obtaininglarger storage capacitance Cstg;

FIG. 16 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a first embodiment of the present invention;

FIGS. 17(A) and 17(B) are sectional views of the storage capacitorportion Cstg taken along line a-a′ in FIG. 1;

FIG. 18 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a second embodiment of the invention;

FIG. 19 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a third embodiment of the invention;

FIGS. 20(A) and 20 (B) are sectional views taken along line 20A—20A inFIG. 16 and line 20B—20B in FIG. 19, respectively;

FIG. 21 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a fourth embodiment of the invention;

FIG. 22 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a fifth embodiment of the invention;

FIG. 23 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a sixth embodiment of the invention;

FIGS. 24(A) and 24(B) are sectional views taken along line 24AB—24AB inFIG. 23;

FIG. 25 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a seventh embodiment of the invention;

FIGS. 26(A)-26(C) are sketches of circled portions “a” at each of whichthe pixel electrode gets over the counter voltage signal line CL, ofFIGS. 14A, 16, 22, in this order;

FIGS. 27 is a plan view of another kind of the electrode structures forreducing the alignment defect during the rubbing treatment;

FIG. 28 is an explanatory figure showing relationship between one ofactual liquid crystal molecules and its model used in thisspecification;

FIGS. 29(A)-29(E) are explanatory figures showing the relationshipbetween the electrode structure and a shape of a protective films formedthereon, FIGS. 29(A)-29(C) show the electrode structure and theprotective film formed thereon in circled portion e of FIG. 14(A), andFIGS. 29(D) and 29(E) shows the improved electrode structure and theprotective film formed thereon;

FIGS. 30(A)-30(E) are explanatory figures showing the relationshipbetween the electrode structure and a shape of a protective films formedthereon, FIGS. 30(A)-30(C) show the electrode structure and theprotective film formed thereon in circled portion a of FIG. 14(A), andFIGS. 30(D) and 30(E) shows the improved electrode structure and theprotective film formed thereon;

FIGS. 31A-31C are cross sectional images for explaining the progress ofthe contamination in the liquid crystal layer that reduces drivingvoltage applied to the liquid crystal molecules;

FIG. 32 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to an eighth embodiment of the invention;

FIG. 33 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a ninth embodiment of the invention;

FIG. 34 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a 10th embodiment of the invention;

FIGS. 35(A) and 35(B) are plan views of two kinds of the electrodestructure for solving the display failure caused by the reduction of theliquid crystal driving voltage;

FIGS. 36 through 38 are partial plan views of the other electrodestructures for solving the display failure caused by the reduction ofthe liquid crystal driving voltage;

FIG. 39 is a cross sectional image for explaining optical transmittancein the IPS-type liquid crystal display device; and

FIGS. 40(A) and 40(B) are a plan view and its cross sectional imageshowing further variation of the invented liquid crystal display device.

DETAILED DESCRIPTION

1. Details of a Liquid Crystal Display Device

First of all, the details of the liquid crystal display device to whichthe inventions mentioned above are applied will be described withreference to FIGS. 2 to 12.

<Sectional Structure of Matrix Area (Pixel Portions)>

FIG. 2 is a sectional view of electrodes for one pixel (FIG. 2(A)) andleft and right side sectional views (FIGS. 2(B) and 2(C)) in an imagedisplay area and substrate peripheral portions of a liquid crystal panelthat constitutes a lateral electric field type liquid crystal displaydevice. FIG. 3 is a sectional view of a thin-film transistor TFT. Asshown in FIG. 2(A), in the lateral electric field type liquid crystalpanel, a thin-film transistor TFT, a storage capacitor Cstg (not shown),and electrodes (a counter electrode CT, a pixel electrode PX, a videosignal line DL, etc.) are formed on a bottom substrate (transparentglass substrate) SUB1. Color filters FIL and a pattern of a light shieldblack matrix BM are formed on a top substrate (transparent glasssubstrate) SUB2. It is possible to form a pattern of the light shieldblack matrix BM on the bottom transparent glass substrate SUB1 asproposed in Japanese Patent Publication No. Hei. 8-806463. An alignmentfilm ORI1 and an alignment film ORI2 for controlling the liquid crystalinitial alignment are formed on the inside surfaces (i.e., the surfaceson the side of a liquid crystal LC) of the respective transparent glasssubstrates SUB1 and SUB2. Polarizing plates POL1 and POL2 are providedon the outside surfaces of the respective transparent glass substratesSUB1 and SUB2 so that their polarizing axes are perpendicular to eachother (crossed Nicols arrangement).

TFT substrate

Next, the components provided on the side of the bottom transparentglass substrate SUB1 (TFT substrate) will be described in detail.

<Thin-Film Transistor>

The thin-film transistor TFT operates in such a manner that thesource-drain channel resistance of decreases when a positive bias isapplied to a gate electrode GT and increases when no bias is applied. Asshown in FIG. 3, the thin-film transistor TFT has the gate electrode GT,a gate insulating film GI, an i-type semiconductor layer AS made of ani-type (intrinsic; not intentionally doped with any conductivity typedetermining impurity) amorphous silicon (a—Si), and a source electrodeSDI and a drain electrode SD2 that are paired. Essentially, the sourceand drain are determined depending on the polarity of a bias that isapplied between them. It should be understood that the source and drainare interchanged because the bias polarity is changed during operationin the circuit of this liquid crystal display device. However, forconvenience of description, the source and drain will be fixed in thefollowing description.

Gate Electrode GT

The gate electrode GT is formed so as to be continuous with a scanningsignal line GL; that is, part of the scanning signal line GL serves asthe gate electrode GT. The gate electrode GT is so formed as to belarger than and hence cover completely the active region, that is, thei-type semiconductor layer AS, of the thin-film transistor TFT (whenviewed from below). Therefore, the gate electrode GT plays not only itsoriginal role but also a role of preventing ambient light and back lightfrom entering the i-type semiconductor layer AS. In this example, thegate electrode GT is a single-layer conductive film g1, which is asputtered aluminum (Al) film, for instance. An Al anodic oxide film AOFis formed on the conductive film g1.

<Scanning Signal Line GL>

The scanning signal line GL is formed in the same manufacturing processas the gate conductive film g1 and is integral with it. A gate voltageVg is supplied to the gate electrode GT from an external circuit via thescanning signal line GL. An Al anodic oxide film AOF is also formed onthe scanning signal line GL. To decrease the probability ofshort-circuiting with the video signal line DL, the scanning signal lineGL is made narrower at the position where it crosses the video signalline DL. Further, the scanning signal line GL is branched into two partsso that even if short-circuiting occurs the short-circuited line can beseparated by laser trimming.

<Counter Electrode CT>

The counter electrode CT is a conductive film g1 that is in the samelayer as the gate electrode GT and the scanning signal line GL. An Alanodic oxide film AOF is also formed on the counter electrode CT. Sincethe counter electrode CT is completely covered with the anodic oxidefilm AOF, it is not short-circuited with the video signal line DL evenif it is made closer to the video signal line DL infinitely.

It is possible to cross the counter electrode CT and the video signalline DL with each other. A counter electrode voltage Vcom is applied tothe counter electrode CT. In this embodiment, the counter electrodevoltage Vcom is set at a potential which is lower than the middle DCpotential of a minimum-level drive voltage Vdmin and a maximum-leveldrive voltage Vdmax that are applied to the video signal line DL by afeed-through voltage ΔVs that occurs when the thin-film transistor TFTis turned off. When it is desired to approximately reduce the powersupply voltage of integrated circuits used in a video signal drivercircuit by one half, an AC voltage may be applied to the counterelectrode CT.

<Counter Voltage Signal Line CL>

The counter voltage signal line CL (see FIG. 1) is formed in the samemanufacturing step as the conductive films g1 of the gate electrode GT,the scanning signal line GL, and the counter electrode CT, and isintegral with the counter electrode CT. The counter electrode voltageVcom is supplied to the counter electrode CT from an external circuitvia the counter voltage signal line CL. An Al anodic oxide film AOF isalso formed on the counter voltage signal line CL. As in the case of thescanning signal line GL, to decrease the probability of short-circuitingwith the video signal line DL, the counter voltage signal line GL ismade narrower at the position where it crosses the video signal line DL.Further, the scanning signal line CL may be branched into two parts sothat even if short-circuiting occurs the short-circuited line can beseparated by laser trimming.

<Insulating Film GI>

In the thin-film transistor TFT, the insulating film GI serves as a gateinsulating film for applying an electric field to the semiconductorlayer AS in cooperation with the gate electrode GT. The insulating filmGI is formed in a layer above the layer of the gate electrode GT and thescanning signal line GL. For example, the insulating film GI is asilicon nitride film formed at a thickness of 120-270 nm (in thisembodiment, 240 nm) by plasma CVD. The gate insulating film GI is soformed as to surround the entire matrix portion AR. Peripheral portionsof the insulating film GI are removed to expose external connectionterminals DTM and GTM. The insulating film GI also contributes toelectrically insulating the scanning signal line GL and the countervoltage signal line CL from the video signal line DL.

<i-type semiconductor layer AS>

The i-type semiconductor layer AS is formed with amorphous silicon at athickness of 20-220 nm (in this embodiment, about 200 nm). Layers d0 aren⁺-type amorphous silicon semiconductor layers for ohmic contact thatare doped with phosphorus (P). The i-type semiconductor layer AS existsunder the layers d0. The layers d0 are left only in areas whereconductive films d1 (and d2) exist over the layers d0.

At the crossing portion of the scanning signal line GL and the videosignal line DL and the crossing portion of the counter voltage signalline CL and the video signal line DL, i-type semiconductor layers AS arealso provided between those lines. These i-type semiconductor layers ASdecrease the possibility of short-circuiting between those lines at thecrossing portions.

<Source Electrode SDI and Drain Electrode SD2>

Each of the source electrode SDI and the drain electrode SD2 is composedof the conductive film d1 that is in contact with the n⁺-typesemiconductor layer d0 and the conductive film d2 that is formed on theconductive film d1. The conductive film d1 is a chromium (Cr) filmformed at a thickness of 50-100 nm (in this embodiment, about 60 nm) bysputtering. The thickness of the Cr film should not exceed about 200 nmbecause the stress increases with the thickness. The Cr film serves toprovide good adhesion with the n⁺-type semiconductor layer d0 and toprevent Al of the conductive film d2 from diffusing into the n⁺-typesemiconductor layer d0; that is, the Cr film is used as what is called abarrier layer.

Other examples of the conductive film d1 are refractory metal films (Mo,Ti, Ta, and W) and refractory metal silicide films (MoSi₂, TiSi₂, TaSi₂,and WSi₂).

The conductive film d2 is formed at a thickness of 300-500 nm (in thisembodiment, 400 nm) by sputtering Al. The Al film can be formed to havea large thickness because the stress in the Al film is smaller than inthe Cr film. The Al film serves to decrease the resistance values of thesource electrode SD1, the drain electrode SD2, and the video signal lineDL and to facilitate covering the steps caused by the gate electrode GTand the i-type semiconductor layers AS (i.e., improve the stepcoverage).

After the conductive films d1 and d2 have been patterned by using thesame mask pattern, part of a film for forming the n⁺-type semiconductorlayer d0 is removed by using the same mask or using the conductive filmsd1 and d2 as a mask. That is, the portion of the film for forming then⁺-type semiconductor layer d0 except the portions under the conductivefilms d1 and d2 is removed in a self-aligned manner. Since the etchingis performed so as to remove the entire thickness of the film forforming the n⁺-type semiconductor layer d0, a slight surface portion ofthe i-type semiconductor layer AS is also etched. The degree of etchingof the i-type semiconductor layer AS may be controlled by the etchingtime.

<Video Signal Line DL>

The video signal line DL is composed of a second conductive film d2 anda third conductive film d3 that are in the same layer as the sourceelectrode SD1 and the drain electrode SD2. The video signal line DL isformed so as to be integral with the drain electrode SD2.

<Pixel Electrode PX>

The pixel electrode PX is composed of a second conductive film d2 and athird conductive film d3 that are in the same layer as the sourceelectrode SD1 and the drain electrode SD2. The pixel electrode PX isformed so as to be integral with the source electrode SD1.

<Storage Capacitor Cstg>

The pixel electrode PX is so formed as to to coextend with part of thecounter voltage signal line CL at its end as shown in FIG. 1. Thiscoextending structure provides the storage capacitor (capacitor element)Cstg having the pixel electrode PX as one electrode and the countervoltage signal line CL as the other electrode. The dielectric film ofthe storage capacitor Cstg is composed of the anodic oxide film AOF andthe insulating film GI that is for example formed as the passivationfilm and used as the gate insulating film GI of the thin-film transistorTFT.

Color Filter Substrate

Next, the components provided on the side of the top transparent glasssubstrate SUB2 (color filter substrate) will be described in detail withreference to FIGS. 2(B), 2(C), and 6.

<Light Shield Film: Black Matrix BM>

The light shield film BM (what is called a black matrix) is formed onthe transparent glass substrate SUB2 to prevent a reduction in contrastratio or the like due to entrance to the display screen side ofunnecessary transmission light coming from gaps other than the gapsbetween the pixel electrode PX and the counter electrode CT. The lightshield film BM also serves to prevent ambient light or back light fromentering the i-type semiconductor layer AS. That is, since the i-typesemiconductor layer AS of the thin-film transistor TFT is sandwichedbetween the light shield film BM and the gate electrode GT that islarger than usual, ambient natural light or back light does not enterit.

The closed, rectangular outline of the black matrix BM shown in FIG. 1indicates the opening in which the light shield film BM is not formed.The same indications as FIG. 1 are employed in the other plan-views ofthe pixel in this specification. The outline pattern shown in thosefigures is just an example.

In the lateral electric field type liquid crystal display device, theblack matrix BM is generally made of a resin composition because itsresistivity should be as high as possible. The Japanese UnexaminedPatent Publication No. Hei. 9-43589 and its counterpart U.S. Pat. No.5,831,701 discloses a proper range of the resistivity of the blackmatrix BM. According to this publication, the resistivity of the liquidcrystal composition LC should be larger than 10^(N) Ω·cm and theresistivity of the black matrix BM should be larger than 10^(M) Ω·cmwhere N≧9 and M≧6. It is desirable that N and M satisfy relationshipsN≧13 and M≧7. Also for the purpose of reducing the surface reflection ofthe liquid crystal display device, it is desirable that the black matrixBM be made of a resin composition.

In contrast to a case where the black matrix BM is made of a metal filmsuch as a Cr film, the use of a resin composition makes a metal filmetching step unnecessary and hence can simplify a manufacturing processof the color filter substrate. Where a metal film is used, themanufacturing process includes 1) metal film formation, 2) resistapplication, 3) exposure, 4) development, and 5) resist peeling. On theother hand, where a resin is used, the manufacturing process includes 1)resist application, 2) exposure, and 3) development. Therefore, theprocess can greatly be shortened.

However, resin compositions have lower light shield performance thanmetal films. Although making a resin film thicker increases its lightshield performance, it increases the thickness variation of the blackmatrix BM. For example, a thickness variation of 10% means a variationof ±0.1 μm when the thickness of the black matrix BM is 1.0 μm and avariation of ±0.2 μm when it is 2 μm.

Further, making the black matrix BM thicker increases the thicknessvariation of the color filter substrate, as a result of which it becomesdifficult to increase the gap accuracy of the liquid crystal displaypanel. For the above reasons, it is desirable that the thickness of theresin film be 2 μm or less.

To provide an OD value of about 4.0 or more with a film thickness of 1μm in a case where blackening is effected by, for instance, increasingthe carbon content, the resistivity of the black matrix BM becomes lowerthan about 10⁶ Ω·cm. Such a black matrix BM cannot be used under thecurrent technological situations. The OD value is defined as the lightabsorption coefficient multiplied by the film thickness.

In view of the above, in this embodiment, the light shield film BM ismade of a resin composition in which a black inorganic pigment is mixedinto a resist material, and is formed at a thickness of about 1.3±0.1μm. Examples of the inorganic pigment are palladium and nickel that isformed by non-electrolyte electrode plating. The resistivity and the ODvalue of the black matrix BM are set at about 10⁹ Ω·cm and about 2.0,respectively.

A calculation result of a light transmission amount that will beobtained when a black matrix made of the above resin composition is usedis as follows.

(OD value)=log(100/Y)  (1)

Y=∫A(λ)B(λ)C(λ)d(λ)/∫A(λ)C(λ)d(λ)  (2)

where A is the luminous efficiency, B is the transmittance, C is thelight source spectrum, and λ is the wavelength of incident light.

When light shielding is effected by using a film having an OD value 2.0,Y=1% is obtained from Equation (1). If it is assumed that the intensityof the incident light is 4,000 cd/m², a transmission light amount iscalculated as about 40 cd/m². This light intensity can notsatisfactorily be recognized visually by a human.

The light shield film BM is also formed in a peripheral area inframe-like form, and the peripheral pattern is made continuous with thepattern in the matrix area having a number of dot-like openings.

<Color Filters FIL>

Color filters FIL are formed as a repetition of red, green, and bluestripes at positions confronting the respective pixels. The colorfilters FIL are so formed as to be laid on the edge portions of thelight shield film BM.

The invention relates to a projected layout of these overlap portions.The details will be described later.

For example, the color filters FIL can be formed in the followingmanner. First, a dyeing base member such as an acrylic resin is formedon the surface of the top transparent glass substrate SUB2, and itsportions not located in the red filters forming regions are removed byphotolithography. Subsequently, red filters R are formed by dyeing theremaining portions of the dyeing base member with a red dye and thenperforming a fixing treatment. Then, green filters G and blue filters Bare sequentially formed by executing similar steps.

<Overcoat film OC>

An overcoat film OC is provided to prevent the dyes of the color filtersFIL from leaking to the liquid crystal LC and to planarize the stepscaused by the light shield film BM. The overcoat film OC is made of atransparent resin material such as an acrylic resin or an epoxy resin.

Liquid Crystal Layer and Polarizing Plates

Next, the liquid crystal layer, the alignment films, the polarizingplates, etc. will be described.

<Liquid Crystal Layer>

The liquid crystal LC is a nematic liquid crystal having a positivepermittivity anisotropy value Δε (called as “a positive dielectricanisotropy”, also) of 13.2 and a refractive index anisotropy value Δn of0.081 (589 nm, 20° C.) and a nematic liquid crystal having a negativepermittivity anisotropy value Δε of −7.3 and a refractive indexanisotropy value Δn (also called “birefringence”) of 0.053 (589 nm, 20°C.).

The thickness of the liquid crystal layer (i.e., the gap) is set largerthan 2.8 μm and smaller than 4.5 μm when the permittivity anisotropyvalue Δε is positive. This is because a permittivity characteristichaving almost no wavelength dependence in the visible range when theretardation Δ·n is larger than 0.25 μm and smaller than 0.32 μm, andthat most of liquid crystals having a positive permittivity anisotropyvalue Δε have a refractive index anisotropy value Δn that is larger than0.07 and smaller than 0.09.

On the other hand, when the permittivity anisotropy value Δε isnegative, the thickness of the liquid crystal layer (i.e., the gap) isset larger than 4.2 μm and smaller than 8.0 μm. This is to make theretardation Δn·d larger than 0.25 μm and smaller than 0.32 μm, as in thecase of liquid crystals having a positive permittivity anisotropy valueΔε. Most of liquid crystals having a negative permittivity anisotropyvalue Δε have a refractive index anisotropy value Δn that is larger than0.04 and smaller than 0.06.

In a state that the liquid crystal layer is combined with the alignmentfilms and the polarizing plates, the maximum transmittance is obtainedwhen liquid crystal molecules are turned by 45° from the rubbingdirection toward the electric field direction. The thickness of theliquid crystal layer (i.e., the gap) is controlled by polymer beads.

The kind of liquid crystal LC is not restricted except that it should bea nematic liquid crystal.

A larger permittivity anisotropy value Δε makes it easier to set thedrive voltage at a smaller value. A smaller refractive index anisotropyvalue Δn makes it easier to set the thickness of the liquid crystallayer (i.e., the gap) larger, whereby the liquid crystal sealing timecan be shortened and the gap variation can be reduced.

<Alignment Films (Orientation Films)>

The alignment films ORI are made of polyimide. The rubbing directionsRDR for the top and bottom substrates are set parallel with each other,and are set so as to form an angle ΦLC of 75° with the applied electricfield direction EDR. This relationship is illustrated in FIG. 4.

The angle between the rubbing direction RDR and the applied electricfield direction EDR may be set not smaller than 45° and smaller than 90°when the liquid crystal LC has a positive permittivity anisotropy valueΔε and set larger than 0° and not larger than 45° when the liquidcrystal LC has a negative permittivity anisotropy value Δε.

<Polarizing Plates>

The polarizing plates POL are G122DU (product name) of Nitto Denko Corp.A polarized light transmission axis MAX1 of the bottom polarizing platePOL1 is set coincident with the rubbing direction RDR and a polarizedlight transmission axis MAX2 of the top polarizing plate POL2 is setperpendicular to the rubbing direction RDR.

This provides a normally closed characteristic in which thetransmittance increases as the voltage applied to each pixel of theinvention (i.e., the voltage applied between the pixel electrode and thecounter electrode CT) is increased.

In the lateral electric field type liquid crystal display device towhich the invention is directed, a display abnormality may occur when ahigh voltage of static electricity or the like is applied externally tothe surface of the top substrate SUB2. Therefore, it is necessary toform a transparent conductive film layer having a sheet resistance ofless than 1×10⁸ Ω/□ above or on the surface of the top polarizing platePOL2, form a transparent conductive film layer of ITO or the like havinga sheet resistance of less than 1×10⁸ Ω/□ between the polarizing platePOL2 and the top transparent substrate SUB2, or mixing conductiveparticles of ITO, SnO₂, In₂O₃, or the like into an adhesive layer of thepolarizing plate POL2 to thereby make its sheet resistance lower than1×10⁸ Ω/□. As for this measure, The Japanese Unexamined PatentPublication No. Hei. 9-105918 discloses in detail a method of improvinga shield function.

<Matrix Peripheral Structures>

FIG. 5 is a plan view showing the main part of peripheral portions ofthe matrix (AR) of the display panel PNL including the top and bottomglass substrates SUB1 and SUB2. FIG. 6 is a sectional view of externalconnection terminals GTM to which a scanning circuit is connected fromthe left side and its vicinity. FIG. 7 is a sectional view of a tapecarrier package TCP shown in FIG. 6.

The display panel shown in FIG. 5 is manufactured as follows. In thecase of a small-size panel, to increase the throughput, one glasssubstrate is divided after being subjected to processing for a pluralityof devices. In the case of a large-size panel, to commonly usemanufacturing facilities, a glass substrate whose size is standardizedfor all product types is processed and then reduced in size so as to besuitable for each product type. In either case, a glass plate is cutafter being subjected to a series of steps.

FIGS. 5 and 6 correspond to the latter case, and show a state that bothof the top and bottom substrates SUB1 and SUB2 have been cut. Symbol LNdenotes edges of those substrates before cutting. In either case, in thecompleted state, the ends of the top substrate SUB2 is located insidethe ends of the bottom substrate SUB1 in portions including externalconnection terminal groups Tg and Td or a terminal CTM (the top portionand the left portion in FIGS. 5) to expose those terminals.

Each of the terminal groups Tg and Td is a collection of a plurality ofconnection terminals GTM for a scanning circuit or connection terminalsDTM for a video signal circuit and their lead-out wiring portions inwhich they are collected for each tape carrier package TCP (see FIGS. 6and 7) on which an integrated circuit chip CHI is mounted.

The lead-out lines of each terminal group extending from the matrix areato the external connection terminal portion are inclined as theyapproach the both ends to adapt the terminals DTM and GTM of the displaypanel PNL to the arrangement pitch of the packages TCP and theconnection terminal pitch of each package TCP.

The counter electrode terminal CTM is a terminal for supplying a counterelectrode voltage to the counter electrode CT externally. The countervoltage signal lines CL of the matrix area are lead out to the side(right side in FIG. 5) opposite to the terminals GTM for a scanningcircuit and are together connected to a common bus line CB, which is inturn connected to the counter electrode terminal CTM.

A sealing pattern SL is formed between the transparent glass substratesSUB1 and SUB2 along their edges so as to seal the liquid crystal LCexcept for a liquid crystal injection inlet INJ. The sealing material isan epoxy resin, for instance.

The alignment films ORI1 and ORI2 are formed inside the sealing patternSL. The polarizing plates POL1 and POL2 are provided on the outsidesurfaces of the bottom transparent glass substrates SUB1 and the toptransparent glass substrates SUB2, respectively.

The liquid crystal LC is sealed in the region partitioned by the sealingpattern SL between the bottom alignment film ORI1 and the top alignmentfilm ORI2 that set the alignment direction of liquid crystal molecules.The bottom alignment film ORI1 is formed on top of the protective filmPSV1 that is formed on the bottom transparent glass substrate SUB1.

The liquid crystal display device is assembled as follows. First,various layers are laid separately on the bottom transparent glasssubstrate SUB1 and the top transparent glass substrate SUB2. After asealing pattern SL is formed on the substrate SUB2, the substrates SUB1and SUB2 are placed one on another. Subsequently, a liquid crystal LC isinjected through an opening INJ of the sealing pattern SL and then theinjection inlet INJ is sealed with an epoxy resin or the like. Finally,the substrates SUB1 and SUB2 are cut.

<Connection Structure of Tape Carrier Package TCP>

As mentioned above, FIG. 7 shows a sectional structure of a tape carrierpackage TCP in which an integrated circuit chip CHI of a scanning signaldriver circuit V or a video signal driver circuit H is mounted on aflexible wiring board and FIG. 6 is a sectional view showing the mainpart of a structure in which the tape carrier package TCP of FIG. 6 isconnected to, in this case, the terminals GTM for a scanning signalcircuit of the liquid crystal display panel PNL.

In FIGS. 6 and 7, an input terminals/wiring portion TTB of theintegrated circuit CHI and an output terminals/wiring portion TTM of theintegrated circuit CHI are made of Cu, for instance. Bonding pads PAD ofthe integrated circuit CHI are connected to inside tip portions(commonly called inner leads) of the portions TTB and TTM by what iscalled face-down bonding.

Outside tip portions (commonly called outer leads) of the portions TTBand TTM, which correspond to the inputs and outputs, respectively, ofthe integrated circuit chip CHI, are connected to a CRT/TFT conversioncircuit/power supply circuit SUP by soldering or the like and to theliquid crystal display panel PNL via anisotropic conductive films ACF.

The package TCP is connected to the panel PNL so that its tip portioncovers the protective film PSV1 of the panel PNL from which theconnection terminals GTM are exposed. Since the protective film PSV1 iscovered with one side portion of the package TCP, the externalconnection terminals GTM (or DTM) are resistant to galvanic corrosion.

Symbol BF1 denotes a base film that is made of polyimide or the like,and SRS denotes a solder resist film as a mask for preventing solverfrom sticking to an undesirable portion during soldering.

The gap between the top and bottom glass substrates SUB2 and SUB1outside the sealing pattern SL is protected by an epoxy resin EPX or thelike after cleaning. The space between the package TCP and the topsubstrate SUB2 is charged with a silicone resin SIL to effect multipleprotection.

<Equivalent Circuit of Entire Display Device>

FIG. 8 is a general circuit diagram of an equivalent circuit of theliquid crystal display device according to the invention. In the liquidcrystal display panel, the image display section is constituted of a setof a number of pixels that are arranged in matrix form. Each pixel is soconfigured as to be able to independently control, that is, modulate,transmission light that is emitted from a backlight provided in the rearof the liquid crystal display panel.

In the active matrix substrate which is one component of the liquidcrystal display panel, the gate signal lines GL and the counter voltagesignal lines CL that extend in the x-direction (row direction) andparallel arranged in the y-direction (column direction) and the videosignal lines (drain signal lines) DL that are insulated from the signallines GL and CL, extend in the y-direction, and parallel arranged in thex-direction are formed in the effective pixel area AR.

A unit pixel is formed in each rectangular region enclosed by a scanningsignal line (gate signal line) GL, a counter voltage signal line CL, anddrain signal lines DL.

The liquid crystal display panel is provided with the vertical scanningcircuit V and the video signal driver circuit H as external circuits.Scanning signals (voltages) are sequentially supplied from the verticalscanning circuit V to the respective gate signal lines GL, and videosignals (voltages) are supplied to the respective drain signal lines DLfrom the video signal driver circuit H with proper timing with respectto the scanning signals.

The vertical scanning circuit V and the video signal driver circuit Hreceive power supply voltages from a liquid crystal driving power supplycircuit 3 as well as display data and control signals that are producedby a controller 2 by dividing image information that is supplied from aCPU 1.

<Driving Method>

FIGS. 9(A)-9(F) shows drive waveform diagrams of the liquid crystaldisplay device according to the invention. A counter electrode voltageis an AC rectangular wave having two values VCH and VCL. Thenon-selection voltage of scanning signals VG(i-1) and VG(i) are variedbetween VGH and VGHL every scanning period in synchronism with thecounter electrode voltage. The amplitude of the counter electrodevoltage is set equal to that of the non-selection voltage.

A video signal voltage is a voltage that is desired to be applied to theliquid crystal layer minus ½ of the amplitude of the counter electrodevoltage.

Although the counter electrode voltage may be a DC voltage, the use ofan AC voltage can decrease the maximum amplitude of the video signalvoltage and enables use of a video signal driver circuit (signal-sidedriver) that is low in breakdown voltage.

<Function of Storage Capacitor Portion Cstg>

The storage capacitor portion Cstg is provided to store videoinformation that has been written to a pixel for a long time (afterturning off of a thin-film transistor TFT).

In contrast to the type in which electric fields develop perpendicularlyto the substrate surfaces, in the type employed by the invention inwhich electric fields develop parallel with the substrate surfaces, apixel electrode and an counter electrode form almost no capacitance(what is called liquid crystal capacitance) and hence the storagecapacitor portion Cstg is an indispensable component.

The storage capacitor portion Cstg also acts to reduce influence of agate potential variation ΔVg on a gate electrode potential Vs when thethin-film transistor TFT is switched. This is expressed by the followingformula:

ΔVs={Cgs/(Cgs+Cstg+Cpix)}×Δvg

where Cgs is the parasitic capacitance formed between the gate electrodeGT and the source electrode SD1 of the thin-film transistor TFT, Cpix isthe capacitance formed between the pixel electrode PX and the counterelectrode CT, and ΔVs is a variation of the pixel electrode potential Vscaused by ΔVg, that is, what is called a feed-through voltage.

The variation ΔVs, which may cause a DC component that is applied to theliquid crystal LC, can be reduced by increasing the storage capacitanceCstg. Reducing the DC component that is applied to the liquid crystal LCis effective in increasing the life of the liquid crystal LC and indecreasing the degree of what is called sticking, that is, a phenomenonthat a previous image remains on the liquid crystal display screen afterswitching is made to a new image.

Since the gate electrode GT is so formed as to completely cover thei-type semiconductor layer AS as described above, the overlap areabetween the gate electrode GT and each of the source electrode SD1 andthe drain electrode SD2 increases accordingly and hence the parasiticcapacitance Cgs increases, which results in a reverse effect that thepixel electrode potential is prone to be affected by the gate (scanning)signal Vg. However, this demerit can be eliminated by providing thestorage capacitor portion Cstg.

<Manufacturing Method>

Next, a description will be made of a manufacturing method of thecomponents on the side of the substrate SUB1 of the above-describedliquid crystal display device.

FIGS. 10-12 show a manufacturing process of the liquid crystal displaydevice according to the invention. In FIGS. 10-12, parenthesizedcharacters at the central part are abbreviated names of steps, andsectional views of a thin-film transistor TFT portion and a gateelectrode terminal and its vicinity both of which indicate a flow of theprocess are shown in the left part and the right part, respectively.Steps A, C in FIG. 10, B, C in FIG. 11, A and B in FIG. 12 correspond torespective photolithography processes and show a state that processingto be executed after the photolithography process has been finished anda photoresist has been removed.

In the invention, each of the photolithography processes means a seriesof operations including application of a photoresist, selected exposureusing a mask, and development. Repeated descriptions of thephotolithography processes will be avoided. Each of steps A-I will bedescribed below.

Step A (FIG. 10):

A 300-nm-thick conductive film g1 of Al—Pd, Al—W, Al—Ta, Al—Ti—Ta, orthe like is formed on a bottom transparent glass substrate SUB1 made ofan AN635 glass (product name) by sputtering. After execution of aphotolithography process, the conductive film g1 is etched selectivelywith a mixed liquid of phosphoric acid, nitric acid, and glacial aceticacid. As a result, gate electrodes GT, scanning signal lines GL, counterelectrodes CT, counter voltage signal lines CL, electrodes PL1, gateterminals GTM, a first conductive layer of a common bus line CB, and afirst conductive layer of a counter electrode terminal CTM, anodized buslines SHg (not shown) that are connected to the gate terminals GTM, andanodized pads (not shown) that are connected to the anodized bus linesSHg are formed. Step B (FIG. 10):

After formation of an anodized mask AO by direct drawing, the substrateSUB1 is immersed in an anodization liquid obtained by diluting anammonia solution of 3%-tartaric acid (pH is adjusted to 6.25±0.05) at aratio of 1:9 with an ethylene glycol liquid and the forming currentdensity is set at 0.5 mA/cm² (constant current forming).

Anodization is continued until the forming voltages reaches 125 V thatis necessary to obtain an aluminum (Al₂O₃) film having a desiredthickness. It is desirable that this state be held for tens of minutes(constant voltage forming). This is important to obtain a uniform Al₂O₃film. As a result, the conductive films g1 are anodized and 180-nm-thickanodic oxide films AOF are formed on the gate electrode GT, the scanningsignal lines GL, the counter electrodes CT, the counter voltage signallines CL, and the electrodes PL1.

Step C (FIG. 10):

A 140-nm-thick ITO film as a transparent conductive film g2 is formed bysputtering. After execution of a photolithographic process, thetransparent conductive film g2 is selectively etched with an etchingliquid that is a mixed acid solution of hydrochloric acid and nitricacid. As a result, uppermost layers of the gate terminals GTM, drainterminals DTM, and a second conductive film of the counter electrodeterminal CTM are formed.

Step A (FIG. 11):

A 220-nm-thick silicon nitride film is formed by introducing an ammoniagas, a silane gas, and a nitrogen gas into a plasma CVD apparatus, andthen a 200-nm-thick i-type amorphous silicon film is formed byintroducing a silane gas and a hydrogen gas into the plasma CVDapparatus. Subsequently, a 30-nm-thick n⁺-type amorphous silicon film isformed by introducing a silane gas, a hydrogen gas, and a phosphine gasinto the plasma CVD apparatus.

Step B (FIG. 11):

After execution of a photolithography process, island-like i-typesemiconductor layers AS are formed by selectively etching the n⁺-typeamorphous silicon film and the i-type amorphous silicon film by usingSF₆ as a dry etching gas.

Step C (FIG. 11):

After execution of a photolithography process, the silicon nitride filmis selectively etched by using SF₆ as a dry etching gas.

Step A (FIG. 12):

A 60-nm-thick conductive film d1 made of Cr is formed by sputtering, andthen a 400-nm-thick conductive film d2 made of Al—Pd, Al—Si, Al—Ta,Al—Ti—Ta, or the like is formed by sputtering. After execution of aphotolithography process, video signal lines DL, source electrodes SD1,drain electrodes SD2, pixel electrodes PX, electrodes PL2, second andthird conductive layers of the common bus line CB, and bus lines SHd(not shown) that short-circuit drain terminals are formed by etching theconductive film d2 with a liquid similar to the liquid used in step Aand etching the conductive film d1 with a solution of ceric ammoniumnitrate.

Then, the portions of the n⁺-type semiconductor layer d0 located betweenthe sources and the drains are removed selectively by etching then⁺-type amorphous silicon film by introducing SF₆ into a dry etchingapparatus.

Step B (FIG. 12):

A 500-nm-thick silicon nitride film is formed by introducing an ammoniagas, a silane gas, and a nitrogen gas into the plasma CVD apparatus.After execution of a photolithography process, a protective film PSV1 isformed by selectively etching the silicon nitride film by using SF₆ as adry etching gas.

FIG. 13 shows a notebook-sized personal computer that is an example ofan information apparatus in which a liquid crystal display device of theinvention is incorporated.

In this personal computer, a keyboard section incorporating a hosthaving a CPU and a display section incorporating a liquid crystaldisplay device are joined to each other by means of a hinge. Displaydata generated by the host of the keyboard section are sent from adriver circuit board PCB3 that is mounted with TCON for performingCRT/TFT signal conversion and generating various timing signals todriver circuit boards PCB1 and PCB2 that is mounted with a pixel driverchip. As a result, an image is generated on a liquid crystal panel PNL.

It goes without saying that the liquid crystal display device of theinvention can be used not only in the above type of notebook-sizedpersonal computer but also other types of personal computers such as adesk-top type one and as other types of monitors.

2. The Electrode Structure in the Pixel

The inventors considered a liquid crystal display device as disclosed inFIG. 15 of PCT gazette WO95/25291 corresponded to U.S. Pat. No.5,786,876 and proposed a liquid crystal display device of IPS typehaving a pixel portion as shown in FIG. 14(A) in order to improve theabove-mentioned storage capacitor portion Ctsg. FIG. 14(A) shows thelayout of electrode formed on the substrate SUB corresponding to SUB1 inFIG. 2.

In contrast to the layout shown in FIG. 1, the proposed structure inFIG. 14(A) has a storage capacitance formed of the overlapping of thepixel electrode PX and a counter voltage signal line CL via insulatingfilm (not shown) in the pixel region. The pixel region is defined by anopening of the black matrix which is a region within a thick-lined framedenoted as BM in FIG. 14(A). The structure is further characterized inthat a cross-shaped pixel electrode has its branches extending from thecrossing so as to overlap the counter voltage signal line. The pixelelectrode PX and the counter electrode CT form an electric field with acomponent substantially parallel to the substrate on which the circuitshown in FIG. 14(A) is formed. The potential of the pixel electrode PXdepends on an output of a switching device (transistor TFT, in FIG.14(A)) controlled by a scanning signal provided by scanning signal line(gate signal line) GL. The potential of the counter electrode CT isdetermined by a counter voltage signal line CL electrically connected toeach counter electrode of the pixels arranged along the scanning signalline GL.

The cross-shaped pixel electrode in FIG. 14A enlarges an area where thepixel electrode PX overlaps with the counter voltage signal line CT toattain higher capacitance for maintaining an electric field applied on apixel region which determines the orientation of the liquid crystalmolecules. Thus, the pixel having the electrodes with a layout of FIG.14(A) can maintain its optical transmittance stable. Furthermore, aseach of the pixel electrodes branches ends in the pixel region (notextending outside of the pixel region), electrical charges can go intoor out from the pixel electrode PX over the counter voltage signal lineCT easily and rapidly when the switching device TFT passes the chargestherethrough. Therefore, the pixel can also respond to the scanningsignal quickly.

In spite of these advantages by the structure of FIG. 14(A), unexpectedfailures are found in controlling the orientations of the liquid crystalmolecules by applying the field. The inventors recognized that aprobability of this failure depends on an intersecting angle definedbetween an extending direction of the branch of the pixel electrode PXand a rubbing direction described later.

As shown in FIG. 14(A) for illustration purposes and which is not drawnto scale, a rubbing treatment is a process to rub a rubbing roller ROLhaving fiber around its circumference against an uppermost surface of asubstrate, which will face to a liquid crystal layer later. Theuppermost surface to be treated is usually formed of an alignment film(also called, an orientation film). In this process, as the rubbingroller moves along the direction shown by an arrow DIR, piles of thefiber around the rubbing roller make dents extending in a predetermineddirection shown as fine stripes on the uppermost surface.

Precisely speaking, the rubbing roller is considered to align thepolymers forming the alignment film, and their alignments depend notonly on the direction DIR but on the rotating direction of the rubbingroller as well. However, fine undulations (corrugations) as shown inFIG. 14(B) (enlarged portion d of FIG. 14(A)) can be observed on theuppermost surface by an atomic force microscope (AFM) after the rubbingtreatment. Thus, the extending direction of the dents in the followingdescription represent the alignment direction of the polymers, also. Onthe other hand, the rubbing direction DIR in the following descriptionsmay deviate from the direction to which the rubbing roller goes on.

In a condition when an electric field is not applied to the liquidcrystal layer or is so faint as to drive liquid crystal moleculestherein for displaying purpose (called a non-field condition,expediently), liquid crystal molecules are oriented along extendingdirections of the dents (the alignment direction of the polymers,mentioned above). Therefore, a result of the rubbing treatment can beevaluated by orientating directions of liquid crystal molecules in thenon-field condition or their variations according to applied fields. Theabove-mentioned orientating directions of liquid crystal molecules inthe non-field condition are also called as “Initial orientating(alignment) direction”.

The failures in controlling orientations of liquid crystal moleculesmentioned before (called “alignment defects”, hereinafter) occur incircled portions “a” and “b” of FIG. 14A where the rubbing roller rollsover the pixel electrode PX or its branches overlapping the countervoltage signal line CL as a result of a step or elevation thereat. Theinventor also proposed another structure as shown in FIG. 15 formingbranches of the counter voltage signal line CL extending up and downfrom its crossing with the pixel electrode PX instead of the branches ofthe pixel electrode PX as FIG. 14(A). Upper and lower ends of branchesof the counter voltage signal line CL are shown by dotted lines in FIG.15. An elevation or step as a result of an overlap of the countervoltage signal line CL and the pixel electrode PX extending from themain surface of the substrate SUB appears at circled portions c in FIG.15 instead of circled portions b in FIG. 14(A). In this structure ofFIG. 15, the alignment defects can be avoided at circled portions a andc looking like circled portions a and b in FIG. 14(A).

According to these results, the alignment defects are considered to becaused by a difference of elevation on a rubbing direction onto asurface of the substrate and an angle defined by an extending directionof the elevation and the rubbing direction.

A fiber on a circumference of a rubbing roller has its pile with a tipof c.a. 20 μm in radius densely. Thus, the circumference of the rubbingroller can be seen as a cluster of spheres having radii of 20 μmarranged thereon from a surface to be rubbed. FIG. 14(C) compares a tipof the piles contacting a substrate surface to a sphere denoted FILhaving radius of “r”. The rubbing roller ROL moves in a direction (shownas an outlined arrow DIR) reversed to its rotation (shown as an outlinedarrow “Rotate”) so as to increase a friction between the pile PIL andthe substrate's surface. The rubbing roller also pushes the pile PILagainst the substrate's surface by applying proper pressure (shown as anoutlined arrow “Press”).

In FIG. 14(C), the rubbing roller ROL is approaching from the left sideof the substrate surface to a bump having a height “h” from the surface.The bump is defined as an elevation formed on the substrate surface andrepresenting a step on the plane to be rubbed, in this specification.Moving the rubbing roller to the right side from the position shown inFIG. 14(C), the pile PIL is pushed up by an upper surface of the bumpand leaves from the surface of the substrate. Then, the rubbing rollerROL moves over the bump. Consequently, the portion of the substratesurface onto which the pile PIL cannot contact or can be hardly pressedeven if it can contact, appears in a length of x extending from the leftedge of the bump. Thus, dents extending along the predetermineddirection as shown FIG. 14(B) cannot be formed or can hardly form asufficient pattern on this portion, so that liquid crystal moleculesfacing this portion cannot be oriented to satisfy the above-mentionedinitial orientating (alignment) direction.

The conventional liquid crystal display device having a structure shownin FIG. 1 covers bumps formed in a pixel region by a pixel electrode PX,etc. with a protective film (an insulating film formed of silicon oxide,silicon nitride, etc.), and limits the rubbing defects around the bumpsso as not to impede the displaying performance. However, the inventorsrecognize that even if the overlapping of the electrode PX and thesignal lines CL in FIG. 14(A) is covered with the protective film, therubbing defects still impedes the displaying performance anddeteriorates the image quality of the liquid crystal display device.

3. Preferred Electrode Structures for Suppressing “Alignment Defects”

Preferred electrode structures for suppressing “alignment defects” arehereinafter described in detail. In the following description,components having the same function are given the same reference symbolin the drawings and will not be described repeatedly.

FIG. 16 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a first embodiment of the invention.

Referring to FIG. 16, when a thin-film transistor TFT that isconstituted of a video signal line DL, a scanning signal line GL, and ana-Si film is turned on, a signal voltage of the video signal line DL istransmitted to a pixel electrode PX and held by a storage capacitorportion Cstg that is composed of an counter voltage signal line CL andthe pixel electrode PX (a dielectric film (insulating film) PS1 formedbetween the counter voltage signal line CL and the pixel electrode PX isnot shown in FIG. 16).

A liquid crystal existing between the pixel electrode PX and the counterelectrode CT is driven by the signal held by the storage capacitorportion Cstg.

The counter voltage signal line CL is located approximately at thecenter of the opening (pixel region) of a black matrix BM, and theinitial alignment direction of liquid crystal molecules form an angle θRwith the counter voltage signal line CL. In general, the angle θR is60°-90°.

FIGS. 17(A) and 17(B) are different possible sectional viewconstructions of the storage capacitor portion Cstg taken along line17AB—17AB in FIG. 16. The capacitor portion Cstg has been previouslydescribed. Therefore, forming the counter voltage signal line CL of asputtered aluminium film, its dielectric film denoted as the passivationfilm PS1 is composed of the anodic oxide film AOF and the insulatingfilm GI in FIG. 12 as the gate insulating film GI of the thin-filmtransistor TFT. As shown in FIG. 17(A), end portions of the countervoltage signal line CL and the pixel electrode PX have respectiveinclination angles θCL and θPX with respect to the surface of asubstrate SUB. This substrate SUB is for example denoted by symbol SUB1in FIGS. 2 and 3, previously. Symbols PS1 and PS2 denote passivationfilms (protective films, i.e., insulating films).

An alignment treatment on the liquid crystal composition is performed insuch a manner that the surface of an alignment film ORI that has beenapplied to the passivation film PS2 that covers the entire substratesurface including the pixel electrode PX (see FIG. 17(A)) with a buffingcloth made of Rayon fiber. Having the layered structure including theelectrode films and the insulating film, the storage capacitor portionCstg is thicker than the other portions in the pixel region (effectivedisplay region) and hence obstructs the liquid crystal alignmenttreatment. That is, in the rubbing treatment in which a roller (rubbingroller) wound with the buffing cloth is moved, while being rotated, sothat the distance from the alignment film ORI is kept such a constantvalue that the buffing cloth is in contact with the alignment film ORI,the rubbing roller runs onto the above step portion. At the peripheriesof the step portion, the buffing cloth does not contact the alignmentfilm ORI normally or the rubbing amount is varied, as a result of whichwhat is called a rubbing defect may occur. The alignment film ORI isdenoted for example by symbol ORI1 in FIG. 2, previously.

In this embodiment, as shown in FIG. 17(A), relationships θPX<θCL and90°<θCL hold and the pattern of the pixel electrode PX (upper layer) andthe pattern of the counter voltage signal line CL are so formed that theoverlapping pixel patterns is within the counter voltage signal linepattern, that is, the projected shape of the counter voltage signal lineCL occupies most of the outline shape of the layered structure thatconstitutes the storage capacitor portion Cstg. Therefore, the boundarybetween the pattern of the entire storage capacitor Cstg and the otherportions in the pixel region is smooth (has a gentle slope) and hencedoes not obstruct the rubbing treatment. The frequency of occurrence ofalignment defects can thus be reduced.

Consider a case such as shown in FIG. 17(B) that the inclination angleθPX is close to 90° or even smaller than 90° and a rubbing defect occursat an end of the pixel electrode PX. Even in this case, if the countervoltage signal line CL is made of an opaque metal material, the rubbingdefect does not affect display because the rubbing defect portion isshielded from light.

FIG. 18 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a second embodiment of the invention.

This embodiment has the same configuration as the first embodiment ofFIG. 16 except that the numbers of comb-teeth portions of pixelelectrodes PX and counter electrodes CT are increased. Thisconfiguration is suitable for a liquid crystal display device having alarge screen.

FIG. 19 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a third embodiment of the invention. FIGS.20(A) and 20(B) are sectional views taken along line 20A—20A in FIG. 16and line 20B—20B in FIG. 19, respectively.

In the first embodiment, as shown in FIG. 16, the portions of the pixelelectrode PX that are connected to the storage capacitor Cstg cross thelevel differences at the peripheries of the counter voltage signal lineCL.

In the portions indicated by symbol a in FIG. 16 (also indicated bysymbol α in FIG. 20(A)) of the pixel electrode PX at the crossingportions, the inclination angle is approximately equal to theinclination angle θCL of the gently sloped peripheries the countervoltage signal line CL (lower layer). Therefore, even the probabilitythat a large level difference causes a rubbing defect is low.

However, in the peripheral portions (indicated by symbol β in FIG. 16;also indicated by symbol β in FIG. 20(A)) of the pixel electrode PX atthe crossing portions, the inclination angle θPX is larger than θCL.Because of the steep inclination in the rubbing direction, a rubbingdefect likely occurs in these peripheral portions.

In view of the above, in this embodiment, the direction θS of theperipheries of the pixel electrode PX at the crossing portions withrespect to the counter voltage signal line CL is made equal to therubbing direction θR as shown in FIG. 19.

FIG. 20(B) is a sectional view taken along line 20B—20B in FIG. 19 thatis parallel with the rubbing direction θR. In the portions indicated bysymbol α in FIG. 19 (also indicated by symbol α in FIG. 20(B)) of thepixel electrode PX at the crossing portions, the inclination angle isapproximately equal to the inclination angle θCL of the gently slopedperipheries the counter voltage signal line CL (lower layer). Therefore,even the probability that a large level difference causes a rubbingdefect is low.

In the peripheral portions (indicated by symbol β in FIG. 19; alsoindicated by symbol β in FIG. 20(B)) of the pixel electrode PX at thecrossing portions where the first embodiment is problematic, there isthe same level difference as in the portions indicated by in FIG. 20(A).However, since the direction θS of the peripheries of the pixelelectrode PX at the crossing portions is made equal to the rubbingdirection θR, the level difference portions (indicated by symbol β) donot obstruct the movement of the rubbing roller. Therefore, thefrequency of occurrence of rubbing defects is low.

FIG. 21 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a fourth embodiment of the invention.

This embodiment has the same configuration as the third embodiment ofFIG. 19 except that the numbers of comb-teeth portions of pixelelectrodes PX and counter electrodes CT are increased. Thisconfiguration is suitable for a liquid crystal display device having alarge screen.

FIG. 22 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a fifth embodiment of the invention. In thethird embodiment, the occurrence of a rubbing defect is prevented byequalizing the direction θS of the peripheries of those portions of thepixel electrode PX that are connected to the storage capacitor Cstg tothe rubbing direction OR at the crossing portions having a leveldifference where those portions of the pixel electrode PX cross thecounter voltage signal line CL.

On the other hand, in this embodiment, a crossing angle θA and a joiningangle θB at wiring crossing portions βand wiring joining portions γ,respectively, that are exposed in the opening of the light shield filmBM are made obtuse angles (smaller than 180°). As a result, thepassivation films can be formed smoothly in the vicinity of the wiringcrossing portions β and the wiring joining portions γ. Therefore, thelevel differences can be reduced and the occurrence of a rubbing defectcan be prevented.

The cross-section of the wiring crossing portions β is the same as thatof the portions β shown in FIG. 20(A) (third embodiment). By virtue ofthe crossing angle θA being an obtuse angle, the passivation film PS2can be formed smoothly and hence the alignment film ORI can also beformed smoothly on the passivation film PS2. Therefore, the movement ofthe rubbing roller can be made smooth and the occurrence of a rubbingdefect can be prevented. Similarly, as for the wiring joining portionsγ, by virtue of the joining angle θB being an obtuse angle, thepassivation films PS1 and PS2 can be formed smoothly and hence theoccurrence of a rubbing defect can be prevented.

FIG. 23 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a sixth embodiment of the invention. FIGS.24(A) and 24(B) are sectional views representing two different possibleconstructions taken along line 24AB—24AB in FIG. 23.

In the storage capacitor portion Cstg shown in FIG. 23, the projectedoutline shape of the pixel electrode PX (upper layer) extends beyond theperipheries of the counter voltage signal line CL (lower layer), tooccupy most of the projected outline shape of the storage capacitorportion Cstg.

In this embodiment, as shown in FIG. 24(A), an inclination angle θPX ofperipheries of the pixel electrode PX is set larger than an inclinationangle θCL of the peripheries of the counter voltage signal line CL(θPX>θCL) and larger than 90° (θPX>90°).

By virtue of the structure that the pattern of the pixel electrode PX(upper layer) extends beyond the counter voltage signal line CL (lowerlayer), the boundary film ORI can be formed smoothly at the boundary ofthe storage capacitor Cstg and hence the occurrence of a rubbing defectcan be prevented.

Consider a case that the inclination angle θCL of the peripheries of thecounter voltage signal line CL is 90° or close to 90° or even smallerthan 90° as shown in FIG. 24(B) and a rubbing defect occurs at portionsof the pixel electrode PX corresponding to the peripheries of thecounter voltage signal line CL. Even in this case, if the pixelelectrode PX is made of an opaque metal material or the like, therubbing defect does not affect display because the rubbing defectportion is shielded from light.

FIG. 25 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to an seventh embodiment of the invention.

This embodiment has the same configuration as the sixth embodiment ofFIG. 23 except that the numbers of comb-teeth portions of pixelelectrodes PX and counter electrodes CT are increased. Thisconfiguration is suitable for a liquid crystal display device having alarge screen.

The preceding first to seventh embodiments are based on the inventorsrecognition that the rubbing defects (causing the alignment defects)depend on mainly a bump existing on the rubbing direction. Thestructural feature common to these embodiments is explained with respectto FIG. 16 which has the most simplified electrode structure in theseembodiments.

As FIG. 16 shows, this common structural feature is to arrange theconductive layers extending along different directions and crossing eachother in the pixel region in the following manner. One of the conductivelayers overlaps with another conductive layer so as to have the outlinethereof within the outline of the another conductive layer at theoverlapping portion, and at least one of the conductive layers extendsalong the direction of another of the conductive layers at theoverlapping portion. Each of the conductive layers represents an objectforming a bump and increasing a height of the bump as a result ofoverlapping with another conductive layer inside a pixel region.Generally speaking, such objects are in the form of conductive layerscarrying electric signals or applying voltage inside the pixel region.

Comparing the structures of FIG. 14(A) and FIG. 16, the portions a and bin FIG. 14(A) causing rubbing defects are represented in FIG. 26(A), andthe portions a and b in FIG. 16 are represented in FIG. 26(B). ComparingFIGS. 26(A) and 26(B), it is apparent that a “terrace” of the countervoltage signal line CL appears on the rubbing direction DIR(Np) in FIG.26(B). If the bump in FIG. 14(C) has a terrace at its side in the mannerof the portion b in FIG. 26B, the rubbing roller can move on thesubstrate surface closer to the bump, and then moves over the terrace.Thus, the distance x in FIG. 14(C) is reduced. Applying this model tothe structure of FIG. 26(B), the rubbing defects around the overlappingof the counter voltage signal line CL and the pixel electrode PX can bereduced sufficiently to prevent the pixel of FIG. 16 from deterioratingits displaying performance and image quality.

Based on this consideration, the structure of FIG. 27 can also providethe same effect as that of the structure of FIG. 16 for suppressing thealignment defects. In FIG. 27, the counter voltage signal line CL hasthe branch portions extending along the pixel electrode PX and havingoutlines within the pixel electrode. Because the branch portions of thecounter voltage signal line CL are disposed under the pixel electrode PX(as shown by dotted rectangles), they form the terraces on the uppersurface of the pixel electrode PX along their outlines. This terraceavoids the alignment defects in the same way as that in FIG. 16.

The structure of FIG. 27 is advantageous to the liquid crystal displaydevice using nematic liquid crystal materials called “Nn-type” as willbe explained below.

In spite of the preceding explanation on the structure of FIG. 15, thealignment defects can increase significantly even in this structure inthe case of using the Nn-type liquid crystal materials, because theprobability of the alignment defects depends on the relationship of arubbing direction and an extending direction of the bump elevated by theoverlapping of the conductive layers.

Liquid crystal molecules generally have structures extending onedirection clearly. FIG. 28 illustrates one of liquid crystal moleculesas an example. This molecule has a fluorine atom and a cyanic basebonded to a benzene-ring (aromatic ring) at its end. In thisspecification, liquid crystal molecules are represented as a cylinder.Liquid crystal molecules are also characterized by their dielectricconstants. There are two kinds of the dielectric constants existing in aliquid crystal molecule, one is denoted as ε₁ in FIG. 28 along a majoraxis of the molecule (the cylinder), and another is denoted as ε₂ alonga minor axis of the molecule. Generally, values of ε₁ and ε₂ aredifferent form each other and the difference called “DielectricAnisotropy” is defined as Δε=ε₁−ε₂.

Liquid crystal materials for IPS-type liquid crystal display devices,generally are of two types of nematic liquid crystal molecules. One is“Np-type” having a larger ε₁ than its ε₂ (thus Δε>0), and another is the“Nn-type” having a smaller ε₁ than its ε₂ (thus Δε<0).

Designing a liquid crystal display device using Np-type liquid crystalmolecules, the molecules are oriented so as to arrange their major axesalong an extending direction of its pixel electrode PX or its counterelectrode CT, or to suppress angles at which their major axes meet anextending direction of the electrode PX or CT display devices.

On the other hand, designing a liquid crystal display device usingNn-type liquid crystal molecules, the molecules are oriented so as toarrange their major axes vertical to an extending direction of its pixelelectrode PX or its counter electrode CT, or to enlarge angles at whichtheir major axes meet an extending direction of the electrode PX or CTdisplay devices.

Therefore, a rubbing direction suitable for the liquid crystal displaydevice using Np-type is different from that for the device usingNn-type. These differences are illustrated in each of FIGS. 16 and 27with an arrow DIR(Np) for Np-type and an arrow DIR(Nn) for Nn-type.Comparing the structures of FIGS. 15 and 27 with attention to therubbing direction DIR(Nn) and referring to the explanation on thecircled portions a and b, it is apparent how alignment defects appear atthe circled portions a and c in FIG. 15.

The important fact to be recognized in both of the structures of FIGS.16 and 27 is that the rubbing roller inevitably moves over theabove-mentioned “terrace” regardless of its direction whenever it movesover the overlapping of the counter voltage signal line CL and the pixelelectrode PX. This fact is also found in the structures of FIG. 22 byapplying the same consideration with FIG. 26(C) as that for FIG. 16 withFIG. 26(B). Forming corners of at least one of the counter voltagesignal line CL and the pixel electrode PX at the crossing portion ofthem with a plurality of obtuse angles as shown in FIG. 22, the“terraces” also appear at the crossing portion as shown in FIG. 26(C).Thus, each of the structures of FIGS. 16, 22, and 27 can suppress theabove mentioned alignment defects regardless of their rubbingdirections. Even if the counter voltage signal line CL is substitutedfor the counter electrode CT, each of the structures also preventsdisplaying performance and image quality of the liquid crystal displaydevice incorporating the same it from being deteriorated by thealignment defects. As mentioned previously, the rubbing conditiondepends on the operating condition of a rubbing roller and the conditionof the protective layer formed between conductive layers crossing eachother and an uppermost surface of the substrate having the rubbingtreatment applied thereto. Therefore, the options to form the side of atleast one of the conductive layers to be slanted by etching, or toextend at least one of the conductive layers along the rubbing directionaround the overlapping portion are also recommended to ensure furtherprevention for the alignment defects.

4. Preferred Electrode Structures for Preventing “Display Failure”

During the consideration for the preceding structures, the inventorsanalyzed the problem of a display failure of a liquid crystal displaydevice caused by deterioration of the maintaining voltage applied to theliquid crystal layer (i.e. the driving voltage of a liquid crystallayer). This problem has been considered to be caused by tracepollutants of the electrode material which dissolve into the liquidcrystal layer as contaminants. Therefore, the problem has beenconsidered to be solved by an aging treatment of the liquid crystaldisplay device to exhaust the dissolvable material. However, the agingprocess actually promotes the contamination, and the region causing thedisplay failure extends in a pixel region along the orientatingdirection of liquid crystal molecules.

Surveying the liquid crystal display devices having a structure of FIG.14(A) and having the above-mentioned display failure, holes were foundon the protective films (insulating films) covering corners ofconductive layers CT, CL, PX in circled portions a and e, respectively.Then, the inventors considered another structure to alter the cornersjoining the counter electrode CT to the counter voltage signal line CLat the portion e. The corner of the another structure has a differentshape as shown in FIG. 29(D) from that shown in FIG. 29(A) utilized inthe structure of FIG. 14(A). The electrode structure shown in FIG. 29(A)is an enlarged image of the corner located left lower part of thecircled portion e in FIG. 14(A). Each of FIGS. 29(B) and 29(E) shows ashape of an insulating film formed over each corner shown in FIGS. 29(A)and 29(D) by chemical vapor deposition.

The active matrix type liquid crystal display has at least two kinds ofinsulating films above its the substrate. One is a protective film PS1(also called “gate insulating film”) to separate a channel of theswitching device (such as a transistor TFT in FIG. 14(A)) for applyingdriving voltage to the pixel electrode PX and a electrode (such as agate line GL in FIG. 14(A)) for controlling the switching device. Achannel is a region through which carriers (electrons or positive holes)pass, and shown as an amorphous silicon region AS of the switchingdevice TFT in FIG. 14(A). The other is a protective film PS2 coveringsuch conductive layers as the pixel electrode, etc. so as to reduceroughness appearing in the uppermost surface of the substrate caused bythese conductive layers. This uppermost surface faces the liquid crystallayer and aligns liquid crystal molecules therein along thepredetermined direction.

Both of the insulating films of FIGS. 29(A) and 29(B) are formed as theformer protective films PS1. As shown in FIGS. 29(A)-29(C), a hole canbe found on the protection film PS1 covering the corner at which thecounter electrode CT joins to the counter voltage signal line CL atright angles. On the other hand, as to the structure as shown in FIGS.29(D) and 29(E) joining the counter electrode CT to the counter voltagesignal line CL via two obtuse angles, no holes appear in the protectionfilm PS1 covering these obtuse angled corners.

Applying the joint structure of FIG. 29(D) to the liquid crystal displaydevices, avoids the above-mentioned display failure.

Furthermore, the inventors considered the shape of the pixel electrodePX in the circled portion a of the liquid crystal display devices shownin FIG. 14(A). The electrode structure shown in FIG. 30(A) is anenlarged image of the corner located in the lower left part of thecircled portion a in FIG. 14(A). In FIG. 30(A), the pixel electrode PXcrosses over the counter voltage signal line CL (in the region PX on CL)and has its branches joining vertically thereto at the crossing portionand extending above the counter voltage signal line CL (in the region PXon CL). These branches (only one of them shown in the left portion ofFIG. 30(A)) face to the counter voltage signal line CT via theprotective film PS1 (not shown) to form a capacitance for maintainingthe voltage of the pixel electrode.

The inventors considered another electrode structure joining the pixelelectrode PX to its branch with obtuse angles as shown in FIG. 30(D),and fabricated both of the electrode structure of FIGS. 30(A) and 30(D),and formed protective films PS2 over both structures by chemical vapordeposition. FIGS. 30(B) and 30(E) show shapes of the insulating films asviewed in the direction of an arrow Obs in FIGS. 30(A) and 30(D),respectively. Holes can be found in the protective film PS2 covering thecorner joining the pixel electrode PX to its branch as shown in FIG.30(A), but cannot be found on the protective films PS2 covering suchcorners as shown in FIG. 30(D).

Applying the joint structure of FIG. 30(D) to the liquid crystal displaydevices also, avoids the above-mentioned display failure.

According to these facts, the inventors recognized that theabove-mentioned display failure by decrease of the driving voltageapplied to a liquid crystal layer might be caused by conducting layershaving different voltages applied thereto and being exposed to theliquid crystal layer via the holes piercing the protective layerscovering these conductive layers respectively. This phenomenon isillustrated in FIGS. 31(A) through 31(C).

First of all, assuming the structure having the counter electrode CTformed on the substrate SUB and covered with the protective films PS1and PS2, and the pixel electrode formed on the protective film PS1 andcovered with the protective film PS2, and applying voltage between thepixel electrode PX and the counter electrode CT as shown in FIG. 31(A),this voltage will be maintained hereinafter in this explanation. Thusthe potential of the pixel electrode PX is higher (positive) than thatof the counter electrode CT (negative). Both of the electrodes PX and CTare exposed to the region called the liquid crystal layer in whichliquid crystal molecules LC are sealed via a hole extending through theorientation film ORI1 and the protective film PS2 or the protectivefilms PS2 and PS1.

In the condition of FIG. 31(A), the material of the pixel electrode PXdissolves as positive ions p-ION into the liquid crystal layer. Assumingthe liquid crystal layer as a solvent, the polarity of the liquidcrystal layer turns to positive in accordance with the amount of thepositive ions therein. Therefore the pixel electrode can hardly produceits positive ions gradually.

But the counter electrode CT of negative potential is also exposed tothe liquid crystal layer, and its polarity turned to positive induce thecounter electrode CT to dissolve as negative ions n-ION into the liquidcrystal as shown in FIG. 31(B). Consequently the contamination of theliquid crystal layer is enhanced, and its resistance drops partially(dark colored region).

The excess of negative ions turns the polarity of the liquid crystallayer and induce the pixel electrode PX to dissolve as positive ionsagain. As FIG. 31(C) shows, the contamination and the resistance drop ofthe liquid crystal layer become significant (as darker colored regionshows), and generate a leakage current between both of the electrodes PXand CT. Therefore, maintaining a voltage difference for controllingliquid crystal molecules' orientation between these electrodes becomesdifficult. For an example of a displaying manner called “Normally blacktype” (reducing optical transmittance of pixel as reducing an electricfield applied to its liquid crystal layer), an unexpected black spotappears in a pixel region passing light therethrough.

The preceding explanation is simplified in terms of steps whereas theactual phenomenon is considered to continuously proceed by variation offine deviation from equilibrium of polarity in the liquid crystal layer.

According to the fact and the phenomenon mentioned above, the inventorshave considered another advantage in the fifth embodiment of FIG. 22. Byvirtue of the crossing angle θA and the joining angle θB being obtuseangles as shown in FIG. 22, the ability of the passivation films PS1 andPS2 of covering the wiring lines and electrodes is increased, whichmakes it possible to prevent a failure of display unevenness due to anelectrolytic reaction between the wiring lines or between theelectrodes.

Therefore, by making the crossing angle θA and the joining angle θBobtuse angles, the voltage reduction in the liquid crystal layer by itscontamination can be prevented and the liquid crystal display device isnot affected by the display failure. If these corners have right angles,the film is not deposited at these corners sufficiently by CVD or thelike and small holes are formed there. These small holes have beenformed to generate the contamination in the liquid crystal layer.

FIG. 32 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to an eighth embodiment of the invention. Thisembodiment has the same configuration as the fifth embodiment of FIG. 22other than the numbers of comb-teeth portions of pixel electrodes PX andcounter electrodes CT are increased. This configuration is suitable fora liquid crystal display device having a large screen. FIG. 33 is aschematic plan view of one pixel that is enclosed by a light shieldfilm, that is, the main structure of a liquid crystal display deviceaccording to a ninth embodiment of the invention. In the sixthembodiment, if right angles or acute angles are formed at the crossingportions β of the counter voltage signal line CL and the storagecapacitor Cstg and the joining portions γ of the pixel electrode PX andthe storage capacitor Cstg as shown in FIG. 23, it is difficult to formthe passivation films PS1 and PS2 smoothly and a rubbing defect mayoccur. Accordingly, in this embodiment, as in the case of the fifthembodiment, the crossing angle θA and the joining angle θB at the wiringcrossing portions βand the wiring joining portions γ, respectively, thatare exposed in the opening of the light shield film BM are made obtuseangles (smaller than 180°). As a result, the passivation films can beformed smoothly in the vicinity of the wiring crossing portions β andthe wiring joining portions γ. Therefore, the level differences can bereduced and the occurrence of a rubbing defect can be prevented.

Further, by virtue of the crossing angle θA and the joining angle θBbeing obtuse angles, the ability of the passivation films PS1 and PS2 tocover the wiring lines and electrodes is increased, which makes itpossible to prevent a failure of display unevenness due to anelectrolytic reaction between the wiring lines or between theelectrodes.

FIG. 34 is a schematic plan view of one pixel that is enclosed by alight shield film, that is, the main structure of a liquid crystaldisplay device according to a tenth embodiment of the invention. Thisembodiment has the same configuration as the ninth embodiment of FIG. 33except that the numbers of comb-teeth portions of pixel electrodes PXand counter electrodes CT are increased. This configuration is suitablefor a liquid crystal display device having a large screen.

Considering the relationship between the preceding results shown inFIGS. 29 and 30 and the phenomenon explained by FIGS. 31(A) through31(C), the inventors recognized that the structures of the fifth,eighth, ninth, and tenth embodiments can be simplified while serving toprevent the display failure mentioned previously. For example, thestructure of the fifth embodiment can be simplified as following twostructures. One structure joins the counter electrode CT to the countervoltage signal line CL at an obtuse angle, i.e. an angle larger than 90degrees as shown in FIG. 35(A), and the other structure forms a cornerappearing in the portion at which the pixel electrode PX crosses over orunder the counter voltage signal line CL, with an obtuse angle as shownin FIG. 35(B).

For explaining the basis for these variations, consideration is given tothe holes on the insulating films as shown in FIGS. 29(C) and 30(C). Asboth a cross sectional image of 29C—29C in FIG. 29(C) and a crosssectional image of plate 30C in FIG. 30(C) show, in the process forforming the protective films on surfaces having a different heights, theprotective film PS1H or PS2H growing on a higher surface covers a lowersurface around the corner before the protective film PS1L or PS2Lgrowing on the lower surface arrives at the corner. Therefore, theprotective film PS1L or PS2L growing on the lower surface cannot arriveat the corner. On the other hand, each of the protective films has itsfront of growth that is curled along arrows shown in its cross section.The curled front of growth prevent each of protective films PS1H, PS2Hgrowing on the higher surfaces from reaching the lower surface even ifit is pushed out from the higher surface and extending above the lowersurface. Such behavior of the protective films prevent both of theprotective films growing on higher and lower surface from joining eachother tightly, and consequently the above-mentioned hole (gap) appearsat the interface between these protective films.

According to this fact, it is necessary to take measures in theviewpoint (1) for suppressing growth rate of the protective film onhigher surface around its corner, and in the viewpoint (2) for promotinggrowth rate of the protective film on lower surface. The viewpoint (1)is to prevent the protective film on the higher surface from beingpushed out extremely at the corner, and the viewpoint (2) is to enable agrowth front of the protective film on the lower surface to reach thecorner before it is covered by another protective film pushed out fromthe higher surface. Both structures in FIGS. 35(A) and 35(B) aresuitable for these purposes.

As to the viewpoint (1), on each surface of two layers joining (see CTand CL in FIG. 35(A)) or crossing (see CL and PX in FIG. 35(B)) at aportion, the protective film grows on independently and extends towardsthe portion (e′ or a′). The protective films grown from these surfacesrespectively run into each other at the portion, accelerate their growthrate, and are pushed out from the surface of the portion finally. Bothof the structures in FIGS. 35(A) and 35(B) enlarge the surface of theportion sufficiently to avoid such a pushing out by setting the joiningor crossing angle obtuse.

As to the viewpoint (2), assuming the surface (SUB) having two objectsjoining (CT and CL in FIG. 35(A)) or crossing (CL and PX in FIG. 35(B))above its surface, two objects become an obstacle for the protectivefilm growing on the rest of the surface (SUB). As shown in crosssectional images of FIGS. 29(C) and 30(C), the growth front of theprotective film is so roundish that it can hardly reach to the corner ofwalls, if the corner is formed by the objects joining or crossing atright angles or an acute angle. As both of the structures in FIGS. 35(A)and 35(B) have the corner formed of obtuse angles, the corner resemblesthe growth front of the protective film rather. Thus, it becomes easierfor the growth front to reach the corner.

Based on above studies, the following structure also can be recommendedfor solving the problem of the display failure.

First, the structures having modified crossing shape of the pixelelectrode PX and the counter voltage signal line CT in a circled portiona′ of FIG. 35(B) are shown in FIGS. 36(A) and 36(B). Both structures arealso suitable to enhance a capacity for stabilizing potential of thepixel electrode (called “additional capacitance” or “storage capacitor”also) by enlarging each portion of the pixel electrode PX and thecounter electrode CT facing via an insulating layer each other.

The structure of FIG. 36(A) joins the pixel electrode to its branches atone obtuse angle for each corner in contrast to that of FIG. 35(B)forming two obtuse angles for each corner. The structure of FIG. 36(B)enlarges the width of the counter voltage signal line CL with its obtuseangled corner around the crossing instead of forming branches of thepixel electrode PX in that of FIG. 35(B). Both structures are alsosuitable for prevention for the alignment defects mentioned previously.

Next, based on the consideration of the viewpoint (2), the number ofobtuse angles in the corner of the joining portions e′ in FIG. 35(A) orthe crossing portion a′ in FIG. 35(B) can increase more than two. FIG.37 shows a part of the structure joining the counter electrode CT to thecounter voltage signal line CL in FIG. 35(A) at the corner consisting ofthree obtuse angles. It is clear from FIG. 37 that by increasing thenumber of obtuse angles in the joining corner, its shape more closelyresembles the growth front of the protective film on the substrate sothat the protective film can reach the corner more easily. Therefore,the corner consisting of infinite number of obtuse angles, i.e. thecurved corner also helps the protective film reach to the corner andprevents a hole from appearing at the corner.

FIG. 38(A) shows the electrode structure having curved corners at thejoining portion e′ of FIG. 35(A) and the crossing portion a′ of FIG.35(B), partially. Further consideration for more preferable conditionfor embodying this structure is mentioned as follows. One of itscriteria is a radius of the curvature of the corner. Consideration forpreferable radii R1 and R2 in FIG. 38(A) is carried out referring FIG.38(B). Extrapolating the edge of conductive layer CL along x-axis andthe edges of conducting layer CT and PX along y-axis, each distance fromthe crossing point of extrapolated lines to the obtuse angle is definedas x_(cor) and y_(cor). In FIG. 38(B), each value has a suffix 1 for theportion e′ or a suffix 2 for the portion a′. Each preferable distance isdefined by the thickness of the protective layer covering the corners,and the thickness is defined for example according to the itsfabrication process. For example, the distances x_(cor1) and y_(cor1)for portion e′ are recommended to be greater than the thickness of theprotective layer PS1 covering portion e′, and the distances x_(cor2) andy_(cor2) for portion a′ are recommended to be greater than the thicknessof the protective layer PS2 covering portion a′. To optimize theseconditions furthermore, considerations on the processing conditions forthese conductive layers are recommended.

Based on present technology, each of these values of x_(cor1), x_(cor2),y_(cor2) and y_(cor2) is recommended to be equal to or greater than 4.3μm or equal to or greater than 5.4 μm. According to such consideration,it is recommended to define the radius R1 in the same way as that forthe distances x_(cor1) and y_(cor1), and to define the radius R2 in thesame way as that for the distances x_(cor2) and y_(cor2) for preferredstructures. Actually, the conditions for the structure of FIG. 38(A) areconsidered to be easier to obtain than those for the structure of FIG.38(B).

Applying this consideration to the structure having more than two obtuseangles in the corner as FIG. 37, the values of x_(cor) and y_(cor) aredefined by the two obtuse angles located both ends of the corner. InFIG. 37, both of the obtuse angle at one end of the corner and that atanother end are indicated by arrows. Setting the values of x_(cor) andy_(cor) greater than the thickness T of the protective layer, these twoobtuse angles are separated by the distance greater than (2T)^(½). Thesame definition in this length as that of FIG. 37 can be applied to thecorner whichever having a plurality of obtuse angles.

There are some possibilities for solving the problem of the displayfailure without employing the aforementioned structure. According to theexplanation based on FIGS. 31(A) through 31(C), there are twoalternative ways for solving this problem. One is to form at least onegroup of (1) the pixel electrode PX, or (2) the counter electrode CT andthe counter voltage signal line CL of such materials called “refractorymetal” as Mo, Ti, Ta, and W or its silicide. Each element or compoundbelonging to this group is considered to dissolve hardly into the liquidcrystal layer. Another is to form one group of (1) the pixel electrodePX, or (2) the counter electrode CT and the counter voltage signal lineCL of a conductive oxide. The conductive oxide like ITO (In₂O₃ dopedwith 1-5 weight % of SnO₂) or SnO₂ hardly dissolves as ions (especially,positive ions) into the liquid crystal layer. Both ways may enable thestructures of FIGS. 14(A), 15, 16 and 27 to be free from the problem ofthe display failure, but also can be combined with the structures ofFIGS. 22, 32 through 38 to confirm their reliability in the productionof the liquid crystal display devices.

In contrast to these alternatives, the structures of FIGS. 22, 32through 38 mentioned above still have great advantages. These structurespermit use of such materials having high electric conductivity as Al,alloy of Al, and Cu, and such adhesive materials to the substrate etc.as Cr for electrodes and lines connected thereto. Although the liquidcrystal molecules having the dielectric anisotropy higher than 20 in theabsolute value are prone to be contaminated easily by the ions dissolvedfrom the electrodes, these structures in accordance with the presentinventions still maintain their reliabilities in avoiding thecontamination of liquid crystal molecules themselves. Therefore, each ofthe above embodiments can provide a liquid crystal display devicecapable of producing good display quality by preventing display failuressuch as a contrast reduction and display unevenness.

5. The Transparent Electrode in the Pixel Region of IPS-type LCD

During the consideration for prevention of the display failure, theinventors considered the IPS-type liquid crystal display device having afeature of forming at least one of the pixel electrode PX and thecounter electrode CT of transparent conductive materials. Such astructure has been already utilized in the liquid crystal display devicecalled “vertical electric field type” in which the counter electrode isdisposed on opposite side of the liquid crystal layer to the pixelelectrode so that the counter electrode faces to the pixel electrode inthe pixel region. However, for the IPS-type liquid crystal display, bothof optical transmittances of the pixel electrode and the counterelectrode are kept lower than in the vertical electric field type.

In the IPS-type, the electric field to control orientation of liquidcrystal molecules LC is applied to the liquid crystal layer so as tohave a main component substantially in parallel to a main surface of thesubstrates SUB1, SUB2, as shown by curved lines with arrows in FIG. 39.Therefore, both of main surfaces of the substrates have spaces in thepixel region above which no conductive layer is disposed andorientations of liquid crystal molecules between these spaces determinean optical transmittance of the pixel region. For this driving manner,the distance W separating the pixel electrode PX from the counterelectrode CT is larger than the closest distance H between thesubstrates SUB1, SUB2 in the IPS-type liquid crystal display device. Aconductive layer in this explanation is defined as the layer of thepixel electrode PX, or the counter electrode CT which is used forapplying an electric field or carrying an electric signal. But there aretwo other layers which may possibly be considered conductive or not. Oneis a light-shielding layer called “black matrix” BM having an openingthat defines the pixel region. Another is a layer called “color filter”FIL surrounded by the black matrix laterally and which transmits lightin a specific wavelength range. In order to forming the electric fieldshown in FIG. 39, it is preferable to keep the resistance of the blackmatrix BM not smaller than 10⁶ Ω/cm, and to keep each resistance of thelayers surrounding the color filter FIL in the pixel region larger thanthat of the black matrix BM.

In spite of these structure, simulated data show that the electric fieldabove the pixel electrode extends almost vertically to the substrateSUB2, like that of vertical electric field type. The density of electricfields above the pixel electrodes higher than that between theelectrodes PX and CT. Therefore, reducing the intensity of incidentlight of hυ_(in) (shown with a size of an arrow) and emitting light ofhυ_(out) between the electrodes PX and CT by controlling the opticaltransmittance of the liquid crystal layer, it is expected that theoptical transmittance above the pixel electrode PX cannot be reduced asthat between the electrodes and the output intensity of hυ_(out)extremely higher (shown with a dotted arrow) than that between theelectrodes. According to this expectation, the light passing through thepixel electrode PX makes gray shade displaying impossible. In spite ofthis expectation, the inventors determined that the pixel electrode PXof transparent conductive material does not affect fine-controlled grayshade displaying function, but rather improve luminance of the pixelregion.

The transparent conductive material mentioned herein is not necessarilya material transmitting incident light thereto completely, and can bedefined as a conductive material having less optical absorption than theother conductive materials disposed around. One of its definitions isdescribed as a material having higher optical transmittance for incidentvisible light than 70% and preferably 80% and electric conductivityequal to or higher than that of semiconductor material. The visiblelight is defined to have its wavelength in a range from 380 nm to 770nm.

As the definition grade of the liquid crystal display device goeshigher, the above mentioned display failure by the reduction of drivingvoltage applied to the liquid crystal layer may appear outside of thepixel region defined by the opening of the black matrix BM. FIG. 40(A)shows the electrode structures of an eleventh embodiment of theinvention suitable for this circumstance. Although the liquid crystaldisplay device of this structure is called IPS-type since a component ofthe electric field is substantially parallel to the surface of thesubstrate, its counter electrodes CT are disposed on opposite side ofthe liquid crystal layer to the pixel electrode. The counter electrodeCT is shown as dot line in FIG. 40(A).

As FIG. 40(B) which is a cross sectional image of 40B—40B in FIG. 40(A)shows, there are spaces under the opening of the black mask BM where anyconductive layer as the pixel electrode PX, the common capacitance lineCC forming a storage capacitance with the pixel electrode, or thecounter electrode CT is not disposed on both of the substrates. Thecounter electrode CT is disposed between two insulating layers OC(explained above) and INS, so as to insulated from the black matrix BM.The pixel electrode PX formed of a transparent conductive material isconnected to the metal layer SD at its end so as to attain an ohmiccontact sufficiently to the channel layer (a-Si) AS of the transistorTFT.

In the higher definition display, many pixels having the electrodestructures are arranged densely to form a pixel array (an entire matrixportion AR, see FIGS. 5, 8). The previous consideration paid attentionto the contamination inside the pixel region. However, the higherdefinition display requires its pixels to be so small and denselyarranged that the contamination may happen between the pixels. Thus, itis necessary to consider conductive layers having corner disposed in thepixel array facing the liquid crystal layer.

Reviewing such a wide range, the voltage differences to be noticedappear between the video signal line (DL) and the pixel electrode PX,between the pixel electrode PX and the common capacitance line CC.Therefore each of the corners in circled portions f, g, j in FIG. 40(A)is formed with an obtuse angle. Forming the pixel electrode PX of atransparent conductive material as ITO, is preferred so as to obtainsufficient luminance from the small pixel, but disposing the metal layerSD between the pixel electrode PX and the transistor TFT is stilleffective. The corners of the common capacitance line CC in circledportion j (forming a T-shaped crossing with the pixel electrode PX) alsoprevent the alignment defects.

The structure of FIG. 40(A) has some points in common with that of thevertical electric field type liquid crystal display. That is, thisstructure can be easily modified to embodying in the vertical electricfield type liquid crystal display. And the structure of FIG. 40(A) willbe effective for the liquid crystal display device of higher definitiongrade than that of XGA-grade (1024 pixels along gate line and 768 pixelsalong video signal line), as UXGA-grade (1600 pixels along gate line and1280 pixels along video signal line). Because the number of pixels alonggate line will be three times of the number defined above in thisstandard, the higher definition standard (especially beyond theUXGA-grade) requires each size of the pixel regions to be smaller.

As already described above, the application range of the invention isnot limited to the above-described lateral electric field type activematrix liquid crystal display device, and the invention can also beutilized to prevent alignment defects of alignment films in the verticalelectric field type or simple matrix liquid crystal display device.

As described above, according to the invention, a liquid crystal displaydevice having good image quality can be provided in which an alignmentdefect does not occur at steps of a storage capacitor portion formed ineach pixel region, the contrast is increased, and there is no displayunevenness.

Finally, each of the discussed structures for solving the alignmentdefects (the rubbing failure), for solving the display failure (thecontamination of liquid crystal layer), and for forming the pixelelectrode of a transparent conductive material can be embodiedindividually or in combinations. However, to meet the demand from theproduction facilities, or the performance required to the liquid crystaldisplay these structures can be combined properly. Any manner of thesecombinations will not deteriorate the merit of each structure to becombined.

What is claimed is:
 1. A liquid crystal display device comprising: firstand second substrates; a liquid crystal composition layer providedbetween the first and second substrates; at least two video signal linesand a scanning signal line formed between the first substrate and theliquid crystal composition layer; at least a counter electrode formedbetween the first substrate and the liquid crystal composition layer;wherein an area between the at least two video signal lines include afirst, second and third region extending along at least one of the atleast two video signal lines; wherein the third region is arrangedaround the scanning signal line and is at least particularly delimitedby the nearest opposite edges of a black matrix portion which extend ina direction of the scanning signal line, the black matrix portion beingarranged over the scanning signal line; wherein the first and secondregions include light transmitting portions therein; wherein said firstand second regions have electrodes therein and a number of electrodes ascounted in a direction of extension of the scanning line in the firstregion is different from a number of electrodes as counted in adirection of extension of the scanning signal line in the second region.2. A liquid crystal display device according to claim 1, wherein atleast one of the first region and the second region is a pixel region.3. A liquid crystal display device according to claim 1, wherein theelectrodes include an electrode having a counter voltage applied theretoand the number of electrodes which have counter voltages applied theretois different between the first region and the second region.
 4. A liquidcrystal display device according to claim 3, wherein at least one of thefirst region and the second region is a pixel region.
 5. A liquidcrystal display device according to claim 3, wherein the electrodehaving a counter voltage applied thereto is a counter electrode.
 6. Aliquid crystal display device according to claim 1, wherein theelectrodes include a pixel electrode and the number of pixel electrodesis different between the first region and the second region.
 7. A liquidcrystal display device according to claim 6, wherein at least one of thefirst region and the second region is a pixel region.
 8. A liquidcrystal display device according to claim 1, wherein the electrodesincludes an electrode having a counter voltage applied thereto and apixel electrode, and the number of electrodes which have counter voltageapplied thereto and the number of pixel electrodes are different betweenthe first region and the second region.
 9. A liquid crystal displaydevice according to claim 8, wherein at least one of the first regionand the second region is a pixel region.
 10. A liquid crystal displaydevice according to claim 8, wherein the electrode having a countervoltage applied thereto is a counter electrode.
 11. A liquid crystaldisplay device according to claim 8, wherein the electrodes include anelectrode having a counter voltage applied thereto and a pixelelectrode, and a distance between the electrodes which have a countervoltage applied thereto and the pixel electrode is different in thefirst and second regions.
 12. A liquid crystal display device accordingto claim 11, wherein at least one of the first region and the secondregion is a pixel region.
 13. A liquid crystal display device accordingto claim 11, wherein the electrode having a counter voltage appliedthereto is a counter electrode.
 14. A liquid crystal display deviceaccording to claim 1, wherein the electrodes include an electrode havinga counter voltage applied thereto and a pixel electrode, and both thenumber of electrodes which have a counter voltage applied thereto andthe number of pixel electrodes are larger in the first region than inthe second region.
 15. A liquid crystal display device according toclaim 14, wherein at least one of the first region and the second regionis a pixel region.
 16. A liquid crystal display device according toclaim 1, wherein said third region is arranged between the first andsecond regions.
 17. A liquid crystal display device comprising: firstand second substrates; a liquid crystal composition layer providedbetween the first and second substrates; at least two video signal linesand a scanning signal line formed between the first substrate and theliquid crystal composition layer; at least a counter electrode formedbetween the first substrate and the liquid crystal composition layer;wherein an area between the at least two video signal lines include afirst, second and third region extending along at least one of the atleast two video signal lines; said the third region is arranged aroundthe scanning signal line and is at least partially delimited by thenearest edges of a black matrix portion extend in a direction of thescanning signal line, the black matrix portion being arranged over thescanning signal line; said the first and the second region include lighttransmitting portions thereon; wherein the first and second regions haveelectrodes therein and a distance between the electrodes in the firstregion is different from a distance between the electrodes in the secondregion.
 18. A liquid crystal display device according to claim 17,wherein the electrodes includes an electrode having a counter voltageapplied thereto and the distance between electrodes which have a countervoltage applied thereto in the first region is different from thedistance between electrodes which have a counter voltage applied theretoin the second region.
 19. A liquid crystal display device according toclaim 18, wherein said electrode having a counter voltage appliedthereto is a counter electrode.
 20. A liquid crystal display deviceaccording to claim 17, wherein the electrodes includes a pixel electrodeand a distance between the pixel electrodes in the first region isdifferent from a distance between the pixel electrode in the secondregion.
 21. A liquid crystal display device according to claim 17,wherein said third region is arranged between the first and secondregions.
 22. A liquid crystal display device comprising: first andsecond substrates; a liquid crystal composition layer provided betweenthe first and second substrates; at least two video signal lines and ascanning signal line formed between the first substrate and the liquidcrystal composition layer; at least a counter electrode formed betweenthe first substrate and the liquid crystal composition layer; wherein anarea between the at least two video signal lines include a first, secondand third region extending along the at least two video signal lines;wherein the third region is arranged around said scanning signal lineand is at least partially delimited by the nearest edges of a blackmatrix portion which extend in a direction of the scanning signal line,the black matrix portion being arranged over the scanning signal line;said the first and the second region include light transmitting portionstherein; wherein the first and second regions have electrodes therein;and wherein an area occupied by the electrodes in a direction parallelto the scanning signal line in the first region is different from anarea occupied by the electrodes in a direction parallel to the scanningsignal line in the second region.
 23. A liquid crystal display deviceaccording to claim 22, wherein the electrodes includes an electrodehaving a counter voltage applied thereto and the ratio occupied by theelectrode having a counter voltage applied thereto is different for thefirst and second regions.
 24. A liquid crystal display device accordingto claim 23, wherein at least one of the first region and the secondregion is a pixel region.
 25. A liquid crystal display device accordingto claim 23, wherein the electrode having a counter voltage appliedthereto is a counter electrode.
 26. A liquid crystal display deviceaccording to claim 22, wherein the electrodes include a pixel electrodeand the ratio occupied by pixel electrodes is different for the firstand second regions.
 27. A liquid crystal display device according toclaim 26, wherein at least one of the first region and the second regionis a pixel region.
 28. A liquid crystal display device according toclaim 22, wherein the electrodes include an electrode having a countervoltage applied thereto and a pixel electrode, and the ratio occupied byelectrodes having a counter voltage applied thereto and the pixelelectrode is different for the first and second regions.
 29. A liquidcrystal display device according to claim 28, wherein at least one ofthe first region and the second region is a pixel region.
 30. A liquidcrystal display device according to claim 28, wherein the electrodehaving a counter voltage applied thereto is a counter electrode.
 31. Aliquid crystal display device according to claim 22, wherein said thirdregion is arranged between the first and second regions.